Part 2 is here: https://www.reddit.com/r/civ/comments/440vzq/how_the_game_works_part_2/
Part 3 is here: https://www.reddit.com/r/civ/comments/44fur0/how_the_game_works_part_3/
Over the past couple months I went from chieftain to emperor difficulty, and a large part of that is me learning a lot about the game, and I want to share some of those lessons. These are factoids experienced players take for granted and new players interpret incorrectly/don't know. Disclaimer: I play with all DLC enabled, this will mostly but not completely apply to the base game. Without further ado, let's dive into it.
Edit: Thank you for all the attention this has been getting! I also have received a lot of useful suggestions in the comments, for which I am thankful, but please make sure that your suggestion is about understanding and using the mechanics of the game, on a more basic level. Not using advanced strategies to gain an edge. This guide is not intended to exploit tricks and abilities, but basic advice how to play the game in general in an optimal way. Thank you.
Growth can be very unintuitive but is also very important. Let's talk about the basics, and work up.
A: Food income. Food is represented by apples. Your city collects food from the terrain, and some buildings also provide food. All this food is your base food, or your food income. Caravans and cargo ships don't count towards your base food. This is the food your city collects every turn.
B: Citizens' food. Every citizen, specialist, farmer, miner, academist, whatever, takes 2 food to live. All this food is subtracted from your food income. So if you have 10 food income, and 4 citizens, those 4 citizens take 8 food to live. You are then only left with 2 food. This is your...
C: Excess food. Your excess food is how much food you are left with after your citizens are done with their meals. This is usually very little. Caravans' and Cargo Ships' food is added to this to get your base excess food. After this, your base excess food is then multiplied by growth rate modifiers. Fertility rites pantheon, and most other things that add a percentage food modifier are multiplied with your base excess food. There are 2 exceptions: Temple of Artemis and the Floating Gardens of the Aztecs are the only modifiers in the game that modify your base food, instead of your excess food. Remember that your base food is usually bigger than your excess food by a factor of 50. Anyway, these modifiers get you your final excess food, which you see in the city screen. Your excess food is then added to...
D: Food Basket. Your city has a food basket, to which your final excess food is added each turn. When the food basket is full, a new citizen is born. The food basket starts off very small, but becomes exponentially bigger with each citizen. Here are the numbers: http://civilization.wikia.com/wiki/Mathematics_of_Civilization_V#Food . You can see that while the second citizen needs a food basket of only 5, the third needs 22, then 30, 40, and quickly you start to need hundreds of turns to fill the food basket for the next citizen. This is why larger cities take so much longer to grow.
Keep in mind that in an unhappy empire, your base excess food is multiplied with 0.25, essentially eliminating growth from your cities. If you have less than 0 happiness, your cities will not grow at all, pretty much.
However, there are some ways to reduce this time. Aqueducts take 40% of the food basket of the previous citizen and add that to the food basket of the next citizen when a new citizen is born. This usually reduces the time you need for the next citizen by 30-40%. That is a lot. You can also increase your base food or your final excess food, to more quickly fill the food basket.
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To recap:
#1 Your city collects food.
#2 Your citizens eat food.
#3 The remainder is added to the food basket each turn.
#4 When the food basket is full, a new citizen is born.
#5 The next food basket is exponentially bigger.
#6 Repeat.
And that is growth.
Happiness is the most important resource in the game. Like growth, we will start at the basics, and work up.
A: What is happiness? Happiness represents how satisfied your citizens are with your rule. Unhappy citizens won't grow, won't work, won't fight, but will sometimes even fight against you. You need to keep your citizens happy to prevent this. Let's go over it now.
B: Luxury Happiness. Happiness comes from each luxury resource you have. Multiple copies of the same luxury do not contribute to more happiness, instead the variety of luxuries matters. Each unique luxury you have gives 4 happiness. When founding cities, make sure you have an average of 1 luxury you didn't already have in that city's range. You can also trade additional copies of luxuries with other civilizations, either for 7 gold per turn (210 gold), or a unique luxury you don't have. Nobody will trade their last copy of a luxury away, and neither should you. Always modify the trade deal to make sure you won't lose your last copy.
C: Building Happiness. Happiness also comes from buildings. Circus, Colosseum, Zoo, Stadium, Broadcast Tower if you have the CN Tower, provide local happiness. Local happiness means that the happiness from those buildings combined can't be higher than the amount of citizens in the city. Basically, if you get 8 building happiness in a city with 5 citizens, you will only get 5 happiness, not 8. You can also get happiness directly from wonders, and that also works this way. Be aware of how much happiness you are losing out on by building the happiness buildings in the wrong cities. Some wonders also produce building happiness.
D: Bonus Building Happiness. Some ideological tenets and wonders increase the building happiness of some buildings. For example, the Neuschwanstein wonder grants +1 happiness for every castle in your empire. That happiness is local happiness as well. Another example is the Socialist Realism tenet in the Order ideology, which gives you 2 Building Happiness for every monument. There are plenty of examples like this. Make sure to grab them if you are having happiness issues. There are also wonders that produce global happiness directly. This is in contrast with the wonders which provide building happiness. There is some inconsistency in the code. If you build your wonders in populous cities however, which you should by the way, then the building happiness limit will usually not apply.
E: Natural Wonder Happiness. Discovering Natural Wonders gives 1 permanent Happiness per natural wonder. It doesn't matter if you were the first or the last either. Make sure to discover as many natural wonders as possible.
F: Unhappiness from Cities and Citizens. In order to prevent civilizations from growing indefinitely, the game gives you unhappiness the more cities and citizens you have. Every city gives you 3 extra unhappiness. Every citizen gives you 1 unhappiness. The more populous you become, and the more wide your empire is, the more unhappy your citizens become. Always keep an eye out for happiness, because you want to keep growing.
G: Unhappiness from Conquest. Capturing a city gives you 3 options. Raze the city, which is like annexing it, but the city will starve by 1 per turn until it is dead. When razed to oblivion, you don't get any unhappiness from it anymore. Puppet the city, which gives you the same unhappiness as normal cities, but you can't control anything in it. Or Annex the city, which gives double city unhappiness (6 unhappiness) and 1.33 unhappiness per citizen. This penalty is due to the Occupied modifier, which a courthouse removes. An annexed city with a courthouse gives the same unhappiness as your own cities. Build or buy courthouses as soon as possible. But you have to wait until the city has stopped revolting, which takes the same amount of turns as there are citizens in the city.
H: Unhappiness from Public Opinion. Ideologies can give you a lot of happiness, but when civilizations with other ideologies have more tourism than you, you will get unhappiness from public opinion. This unhappiness can be impossibly high and absolutely crippling if other civilizations have high influence over you. When you have citizens unhappy with your ideology (you don't need to be in negative happiness for this to be possible) you can always switch ideology to the ideology that is the most culturally influential over you. This gives you a few turns of anarchy, where your cities will do absolutely nothing, and then all happiness from ideological pressure is removed. But so is the happiness from your ideological tenets, as well as all other benefits. You will get free tenets to invest in the new ideology, but one less than you invested in the previous ideology. Free tenets from being an early adopter do not apply. But you may have to switch. Your cities may flip to other civilizations if you are unhappy enough too.
I: Effects of Unhappiness. Being unhappy comes with bad modifiers to your entire empire. Your growth rate is modified by -75%. This means your cities will pretty much not grow at all. They won't starve because of this, but you cannot grow when you are unhappy. Unhappiness also gives -2% gold output, -2% production output, and -2% combat strength.
Getting -10 unhappiness or more makes your civilization "Very Unhappy", which is much more severe. You won't grow at all any more. Absolutely no growth. Also, you can't train settlers, and you will regularly get rebellions, which means barbarians of your technology level will spawn around your cities. And the production, gold, and combat strength penalties keep decreasing at the same rate (-2% per unhappiness).
Getting -20 unhappiness is crippling. This is usually due to Public Opinion, with your cities regularly switching to civilizations with the preferred ideology. This will pretty much ruin your empire. At this point you need to either get amazing happiness boosts, eliminate the offending tourism-heavy civilizations, or change ideology.
J: Golden Ages. On the other side of the spectrum, having positive happiness gets you to golden ages faster. Each turn, your happiness contributes to a golden age counter, in a very similar way to growth in cities. A golden age requires golden age points, which happiness contributes to. You can also get golden ages from wonders, social policies, and Great Artists. A Golden Age gives you a 20% production and culture boost. It also gives tiles which produced at least 1 gold before the gold age, 1 gold extra. Note this doesn't mean double terrain gold output, because a 2 gold tile will only produce 3, a 4 gold tile produces only 5, etc... Still a nice benefit, but not as powerful as it sounds. There are also civilizations which gain additional benefits from golden ages, like Persia and Brazil. Golden ages last 10 turns by default, which can be increased through various means. Golden Ages from Great Artists last 8 turns, which are also modified by those modifiers. More than 0 happiness gives no extra bonuses during a golden age, the next golden age counter will start right where it was when the golden age came into effect. If the golden age was acquired through golden age points, it will start at 0 golden age points again. Golden Ages triggered through other means will simply let golden age progress from where it was interrupted. Every new golden age will take more golden age points than the previous one.
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To recap:
#1 Unhappiness stops growth.
#2 Unhappiness gives production, gold, and combat penalties.
#3 Severe unhappiness spawns modern barbarians and triggers cities leaving your empire.
#4 Unhappiness is generated by the number of cities and citizens.
#5 Annexed and currently razing cities give more unhappiness than your own.
#6 Civilizations with more tourism than you and a different ideology than you trigger unhappiness from public opinion.
#7 Happiness is used to counter Unhappiness.
#8 Happiness comes from unique luxuries available to your empire.
#9 Happiness is also generated by buildings.
#10 Ideological Tenets provide a lot of additional Building Happiness.
#11 Building happiness is limited by the citizens in the city.
#12 Wonders can provide both global and building Happiness.
#13 Positive happiness contributes to golden ages.
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And that is Happiness.
Science is crucial to getting an advantage. Those who fall behind will remain in the annals of history. Let's dive into the beaker.
A: Population. The lion's share of your science will come from your population. Every citizen produces 1 science by default. This can be increased to 1.5 with a library, and 2 with a public school. Although that is a significant bonus, what is very important to remember is that population drives science. The more citizens, the more science. You cannot get away from this. If you want to have any science, you have to get population.
B: Specialists. What many new players forget to do is work specialist slots. It is very important to work scientist slots to increase your science output. Whereas most citizens will produce only 1.5 science by the time your first scientist slots are available, specialists produce 3 science, which can become 5 with the Secularism social policy in Rationalism. That is at least double. Don't forget that scientists are also citizens, so scientists actually produce 4.5 science, which would be triple. You can at most only work 4 scientist slots at a time per city, but they still provide a large boost. Sometimes you need those citizens somewhere else, but if you can, work those scientist slots. Scientist also provide Great Scientist points, increasing your spawn rate of them. Make sure to get Great Scientists, because you can plant them to get...
C: Science Tiles. There are 3 types of terrain that produce science. These are some natural wonders, jungle (if the city has a university), and academies. Before the industrial era you almost always want to plant great scientists into academies. It is recommended to do this on a tile without resources, that you normally won't work. Usually plains/grasslands without fresh water (fresh water means adjacent to a river or a lake). The best place is the grasslands without fresh water, because that citizen will feed himself (grasslands with academy provides 2 food + the academy yield). It is also very crucial to cut down as few jungles as you have to. Jungles provide at least 2 food and 2 science when you have a university. Sometimes you have to build mines on a jungle hill to get any production in that city, but usually you want to build trading posts in jungle to get a tile that provides 2 food, 2 gold, and 2 science (3 science with Free Thought policy). Brazil should build brazilwood camps instead, which provide culture as well.
D: Modifiers. All the science produced in the sections A, B, and C, adds up to your base science. This base science is added on with some buildings and wonders, but they usually don't have a very large impact. This base science is then multiplied by some modifiers. These modifiers can really stack up to ridiculous numbers. Let's go over them. The University provides a 33% modifier, which becomes 50% with the Free Thought policy. The Observatory requires the city to be adjacent to a mountain, but provides another 50% modifier. You usually want cities adjacent to mountains if you plan on playing tall because of this. The research lab is very expensive (4 maintenance), but adds another 50% modifier. There is a tier 2 tenet in the Order ideology that makes factories provide another 25% modifier. This may convince you to choose order if you are playing tall. Finally, the city with the National College gets another 50% modifier. In total, this is a 150% modifier at least, which is 200% in the city with the national college, and 175%/225% if you have the Order tenet. Take that in for a moment. You should expect about 400-500 science in your capital, and 150-200 science in your bigger cities (10+ population), if you completely optimize your science output. With 3-6 cities, that can be 1500-2000 science per turn in the modern/atomic era.
E: Research. So what does all this science do? Every turn, science is invested in a particular technology. All technologies have a base science cost. This cost is increased by 2% for every city you own (actually the highest number of cities you ever owned at any particular turn in that game), and decreased by the amount of civilizations, you have met, who have already researched that technology. All technologies in the same column (in the technology tree) cost the same base amount, which increases exponentially the deeper in the technology tree you go. Once you have invested more science in a technology than the science cost of said technology, the technology gets discovered, you unlock the abilities that technology provides, and the remaining science is added to whatever technology you are researching at the end of your turn, in addition to the science you made that turn as well.
You can also get additional science on occasion through a variety of methods. Let's go over those as well.
F: Bulbing. "Bulbing" means using your Great Scientists to discover a technology. This doesn't actually discover any particular technology, but invests the science you generated in the previous 8 turns in whatever technology you are currently researching. This means it is usually a good idea to store your scientists generated after the industrial era until you have built research labs in your primary science cities 8 turns ago, so you get the most bang for your buck. Be aware that you cannot boost this to infinity by bulbing a Great Scientist every turn, to exponentially increase the science gain. Bulbing a great scientist directly invests the science into technologies, and bulbing takes a look at your science output. So make sure you have your tech path set before you bulb your great scientists. Bulbing also doesn't care about the science you lose due to budget deficits. Just an interesting factoid.
G: Technology. Technologies are sorted in a tree-like structure, where each technology has at least one technology you have to research before that, with the exception of Agriculture which every civilization gets for free. This means that you can't start researching advanced technologies before you have figured out the basics. But you can go very deep into the technology tree before you have to research some more trivial technologies. For example, you can research Archaeology without researching Mining. And you can research Fertilizer without researching Pottery.
H: Optimal pathing. It is very important to optimize your technology by researching technologies that give you the best advantage first, so research is quicker. One common strategy in single-player is to research Pottery-Writing-Calender-Philosophy to get a National College really quickly. The downside to this strategy is that you aren't researching anything that helps you right now, so your warrior will have to defend your empire in the meantime for example. It is usually a good idea to get important technologies early to help your empire now, and then focus your science on the future while you can at least somewhat defend your empire with archers and get infrastructure like pastures and mines constructed in the meantime. Make sure to put thought into your technology path, because what is best in the general case might not be best for you in your situation.
For example, technologies like Civil Service also boost your science, because they increase food, which increases growth, which increases population, which increases science. But sometimes you can spawn next to an aggressive neighbour and need to get military technologies like Construction and Bronze Working earlier than you might have wanted to. Or maybe you are the aggressive neighbour and want to surprise your opponent. These considerations also factor in the more late-game as well, where you want the technological advantage to surprise your opponent with a certain unit they haven't built defences against. Make sure to plan your technologies around free technologies like the finisher in Rationalism or the Oxford University national wonder. Key scientific technologies to acquire are usually: Writing, Education, Scientific Theory, Plastics, Satellites. Satellites in particular requires you to ensure you get the Hubble Space Telescope.
I: Rationalism. Rationalism is a social policy tree that is absolutely essential for science. It provides 10% extra science when you have 0 or more happiness (opener), it provides 2 extra science for every specialist (Secularism), it provides 1 extra science for every trading post and 17% extra science modifier from universities (Free Thought), it provides 25% more Great Scientist generation (Humanism), it provides 50% more science from research agreements (Scientific Revolution), it provides 1 extra gold from libraries, universities, public schools, and research labs (Sovereignty), and it provides a free technology and the ability to spend faith on great scientists (finisher). That is an amazing amount of science. Put together, this tree probably provides 80%-125% more science than if you weren't to open it. Especially if you use the ability to purchase great scientists with faith. If you care about science at all, and you should, make sure to get this tree.
J: Research Agreements. Research Agreements can be made with civilizations you have a friendship with when both you and the other civilization have researched Education and you are both able to afford the investment. When the research agreement ends, you and the other civilization get 50% of the median science value of all the technologies you can choose to research at that turn. The Porcelain Tower world wonder and the Scientific Revolution social policy both increase the bonus by 50%. Research Agreements usually provide more raw science for the more advanced civilization, but is usually balanced since the science is based on the cost of the technologies. When you and the other player come at war with one another, or one of the civilizations is wiped out, the research agreement is lost, no science is made, and the gold is not retrieved.
K: Espionage. Spies are available for everyone once anyone enters the renaissance era. You get one spy for every era you enter after that. Entering the classical, medieval, or renaissance era after someone has entered the renaissance era will not grant additional spies. Spies in foreign cities who have researched technologies you haven't will attempt to steal a technology. Stealing a technology involves waiting a number of turns, depending on the science output of that city and the technology difference between you and the other civilization, after which the spy is either discovered and killed, or you are able to steal a technology, which involves you choosing a technology they have that you don't have but do have the prerequisite technologies for. When discovered, you will gain a relations penalty with the civilization in question. You can put spies in your own cities to increase the chance of discovering enemy espionage against you. You can also construct Constabularies and Police Stations to delay the stealing process. The highest science output, and therefore the quickest to steal from, will usually be in the capital, although high population cities can also be viable targets.
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To recap:
#1 Population creates Science.
#2 Scientist specialists create a lot of Science and generate Great Scientists faster.
#3 Jungle produces Science with Universities.
#4 Science Buildings make your Science yield ridiculous.
#5 The Rationalism Social Policy tree provides even more Science.
#5 Science is invested into Technologies at the end of every turn.
#6 You cannot research technologies if you have yet to discover the prerequisite technologies.
#7 Technologies are discovered when the Science invested is greater than the Science cost of that Technology.
#8 Bulbing Great Scientists invests the Science made the past 8 turns (on Standard speed) in the Technologies you are researching.
#9 Choosing your Technology Path to optimize gaining abilities with researching more technologies is important.
#10 Research Agreements can provide additional Science.
#11 Spies can attempt to steal technologies from more advanced civilizations, at the risk of a diplomatic penalty and/or losing the spy in question.
#12 Finishing Rationalism and constructing certain wonders grants additional Great Scientists.
#13 Finishing Rationalism allows the purchase of additional Great Scientists with Faith.
And that is Science.
Production is crucial to assembling your infrastructure and military. Without it, you are useless. Let's dive in.
A: Terrain. Terrain is the main source of your early production. Hills always have at least 2 production, and forests and plains always have at least 1 food and 1 production. Flat Grasslands, Jungle, Tundra, Snow, Desert, and Coast does not have production. There are ways to get production in those situations, either through some strategic resources, which always provide +1 production, and another one once improved buildings. For example, the Seaport provides +1 production to all coastal resources. But usually, production is hard to come by in those areas. You can always cut down Jungle to reveal the plains tile beneath it, but that costs you 2 Science, which is a hard bargain. Grasslands without a resource cannot provide production. Pasture resources will allow you to get some additional production on grasslands as well. Snow, desert, and tundra usually leave you crippled. Although the Petra wonder gives every desert tile that is not Flood Plains (which have +2 food) one additional food and one additional production, there can only be one city with the Petra, and desert cities usually aren't very strong either, so getting the Petra in the first place can prove difficult.
But usually, you will have to resort to hills for production. A 2 production tile is pretty good, and it can be even better with resources. Sheep provide +1 food, and Copper, Gold, Gems, and Silver provide some bonus Gold. Strategic resources provide +1 production (+2 as Russia). Then, you want to improve the tiles. All hills (except for sheep and horse hills) can be improved with a mine. A mine adds +1 production. That means any hill can produce 3 production, and usually they have some bonus in addition to that.
Forests can also provide 1 Food and 2 Production when they have a lumber mill, but forests can also provide a one-time production boost to the nearest city you own. Usually you want to cut down forests for a production boost if you have plenty of hills nearby to work instead, but when you don't have hills to fall back on, it makes more sense to keep forests around.
Finally, there are Stone and Marble resources which provide +1 production and can be improved with a quarry, which provides another +1 production, after which you can construct a Stone Works in the city, which provides yet another production for those tiles, as well as a bonus Happiness in that city. That adds up to +3 Production on Marble and Stone when improved.
Later technologies in the Industrial era improve almost all improvements with their relevant yield type. But at that point your cities will probably have plenty of...
B: Buildings. There are a couple strong buildings that improve the production output of cities. Most provide additional production when the city is building something specific, but some always provide additional production. Early on, you will have the Stable, the Lighthouse, and the Stone Works. These three buildings give their relevant resources +1 production. In the medieval era, you have the Workshop. The Workshop gives you 10% extra Production output in general. That does not sound like much now, but it will be a big difference when you start amassing more production. It also allows that city to send production caravans and cargo ships, which increase the final production in their destination city. This is important to help out those production-hungry cities we discussed earlier.
When you advance into more modern eras, the production output of your cities increases dramatically. First of all, Chemistry gives every mine and quarry +1 production. That is probably a 20%-30% increase in your cities's production output. Then you get industrialization. This unlocks a new strategic resource, coal, which provides +1 production now that you know it. But much more importantly, for 1 coal per factory, you can increase the production in all your cities with a workshop by a base of +4 and then +10% Production again. River cities can also create a hydro plant, giving 1 additional production on every tile adjacent to a river. This is unlocked with Electricity. Coastal cities can get a seaport at Navigation, improving coastal resource yields with +1 production and +1 gold. In the Atomic era, you will also have access to Solar Plants and Nuclear Plants, which are exclusive, but both provide +5 base production and +15% Production efficiency. Adding together all the modifiers, that is +10% from the workshop, +10% from the factory, and +15% from either one of these, makes +35% production efficiency in your cities. Not to mention Chemistry, Scientific Theory, and a Hydro plant if applicable, which give +50% production yields on average. Considering your base production will probably be about 50 at this time, that will all make a big difference. Your production will increase a lot through the later eras. Granted, you probably won't build Nuclear plants or Solar plants in your cities due to time constraints, but you probably will in your bigger cities, where it will have more of an impact.
C: Production Focus. Now on to an important technique that seems like an exploit but is crucial to getting production early in the game. Set your city to Production focus. When a new turn starts, the game will take a look at how much food you are making that turn, and puts that in the basket. If the basket is full enough, a new citizen is born. That new citizen will then get assigned according to your focus in that city. It would probably work a food tile on default focus, but the game has already calculated food, so that won't count that turn. Once the citizen has been assigned, it then calculates production. If you have your city on production focus, it will assign the new citizen to the highest-production tile it can work, and that production will be calculated in. This is why you set your city to production focus. To make sure you get the most bang for your buck with that citizen. It is important to then manually lock the tiles you want that city to work when you can do stuff again. Later on, when you don't want to bother with so many citizens, the production focus will ensure the new citizens will make your cities as powerful as they can be. It is also a good way to teach the habit of manually assigning tiles. This micromanagement is very important to maximize your gains and minimize the amount of turns wasted.
D: Construction. Now on to applying production. Everything that a city can build has a certain hammer cost associated with it. When you are building something in a city, the production output of that city on that turn will be used to fill up a meter, in much the same way the food basket works. You can switch production mid-way through to something else and you will not lose your progress. Excess production not needed to finish the meter on the turn the construction was finished will be applied to whatever you are constructing next. You can also choose to construct gold, when you have researched guilds, or research, when you have researched education. If you construct that, 25% of your city's production output is instead converted to gold or science, respectively. If the World Congress has passed the World's Fair, the Olympic Games, or the International Space Station, you can also have your cities construct that. When they are contributing to that, they will use all their hammers as opposed to the 25% hammers used to construct gold or science.
E: Great Engineers. Just like the Great Scientist is the Great Person related to Science, is the Great Engineer the great person related to Production. Great Engineers can be either planted as a manufactory, providing +4 production to that tile, or spent to hurry production, massively increasing production output in a city on that turn depending on that city's population. Creating a manufactory can be really advantageous in otherwise production-hungry cities, since it will give that city the production it needed to get going, and it will provide a nice amount of base production for that city in the long run too. Choosing the location to plant a manufactory is usually done in a similar fashion to planting an academy. You don't want to work a tile you normally wouldn't, but neither would you want to take up a tile that could have a large yield in its own right. Usually, a non-fresh water grasslands or plains tile without a resource is the best desicion, although it can make sense to connect up a strategic resource, which would save you the time it would normally take to construct the improvement. Alternatively, and the way the Great Engineer is used the most, is to rush a World Wonder. A lot of World Wonders provide really nice benefits, but there can only be one World Wonder in the world. A Great Engineer can greatly increase your chances of acquiring that World Wonder by giving you a big headstart on the production of that wonder. In fact, it usually provides so much production the wonder will be done the following turn. The amount of production the Great Engineer provides is solely dependent on the population of that city. Nothing else. If you have unlocked the Spaceflight Pioneers tenet in Order ideology, you can also use Great Engineers to rush the production of spaceship parts. This can be exceptionally helpful in scientific empires which have a lot of growth but not a lot of production.
Great Engineers can be obtained through Faith if you have finished the Tradition social policy tree, and otherwise Great Engineer points can be obtained by working Engineer specialist slots, in the Workshop, the Factory, and the Windmill. Please note that acquiring Great Engineers through great person points also makes the next great scientist, great merchant, or great engineer more expensive. The same is true of great scientists and great merchants. Acquiring them through faith does not have this drawback.
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To recap:
#1 Production comes mainly from Hills and Forests.
#2 Strategic Resources and Improvements can increase Production output.
#3 Chopping down a Forest grants a one-time Production boost to the nearest city you own.
#4 Production buildings increase either the Production your tiles provide or increase the Production efficiency of the city.
#5 Always set your cities to Production Focus.
#6 All things a city can construct have a set hammer cost.
#7 Every turn, the Production of a city is added to the meter of what a city is constructing at that time.
#8 When the meter for a construction is above the hammer cost of that construction, the construction finishes and the remaining production is added to what that city constructs at the end of the turn.
#9 Working engineer slots provide Great Person points towards a Great Engineer.
#10 A Great Engineer can construct a Manufactory for a constant production bonus.
#11 A Great Engineer can hurry production to add a lot of Production to a city depending on the population of that city.
#12 Using hurry production on a World Wonder usually gives you a great shot at securing it for yourself.
And that is Production.
Okay, apparently I have a maximum of 40000 characters in one self-post. Who knew. I will link to the second part, covering Culture and Tourism here: https://www.reddit.com/r/civ/comments/440vzq/how_the_game_works_part_2/
You can read about Religion here: https://www.reddit.com/r/civ/comments/44fur0/how_the_game_works_part_3/