Hello again, everyone!

I played the first 16 turns of the game tonight, but I will only be posting a summary of the first turn and a detailed explanation of some game concepts that will help us later on. Here it is:
TURN 0
- [UNIT] Warrior moved SW
- [UNIT] Settler build city - Carthage founded - queue Warrior
On the first turn, I decided to simplify things by just plopping down immediately where the computer placed me. Carthage is founded! Hurray!

The city immediately starts production of a second Warrior unit (we started the game with one Warrior already). At this stage in the game, my goal is to get out there and explore as much as I can. Exploring serves three purposes - meeting other civilizations, scouting the land for resources, and finding village huts.
Before we finish the first turn, I want to take a few moments and describe an extremely critical concept in Civ 4, one that is rarely understood quickly by new players (including myself back when I first started): Commerce.
Commerce is represented by a little coin icon

commerce

in a city screen. Let's open our city info screen to learn a little bit more about how commerce works. You can open the city info screen of any city by double-clicking the city on the map (just above the city name).
Before diving into the guts of commerce, let's step back for a moment and take a look at the concept of city management in general. Even if you are a newbie, you have probably figured out much of this already, but I don't want to assume so I'll go through it anyway.
Notice the two white circles within my city screen. Those circles represent the tiles that my population is "working" for food

food

, production

hammers

, and commerce

commerce

. You get to work the tile your city is founded on for free, and then you get an additional tile for each point of population in the city. Because Carthage is population 1 (shown at the top as "Carthage: 1"), that means I can work a total of 2 tiles: the city tile, and one other tile of my choosing. If you never mess with this screen, the governor (AI) will automatically select which tiles your citizens will work, but you can always override this at any time. Currently, my governor has selected the oasis tile just south of my city as the tile my 1 population will work.
Between the two tiles, I am producing 5 food, 1 production, and 4 commerce. Food and production are fairly simple. You need to feed each population point 2 food per turn. In order for your city to grow, you must make more food than the bare minimum needed to feed your population. The greater the surplus food you have, the faster your cities grow. Production is used to produce whatever is in your build queue. Each item has a cost in production points, and each production point you gain from working tiles is applied to that cost every turn until the cumulative production exceeds the cost. For instance, if my city produces 2 production points per turn and my item costs 10 production points, then I will build that item in 5 turns (10 / 2 = 5).
Commerce, however, is a bit trickier. Commerce isn't directly used by a city. Instead, it is converted into some other benefit for your empire as a whole. This early in the game, your commerce can only be converted into research

science

or gold

gold

. Later on, after discovering any other civilization, it can also be converted to espionage

espionage

. Still later, after discovering the Drama technology, commerce can be converted into culture

culture

as well.
Going back to the city info screen, I can manually override my governor's selection of tiles to work simply by clicking another tile. The little white circle will then move to that tile, indicating that it is being worked now. Let's try some different tiles and see the effect on my city output.
By working the plains hill tile, my city produces a total of 2 food, 3 production, and 1 commerce from tiles. Notice that the little food bar now says "Stagnant" - this is because I am not producing any more than the bare minimum amount of food needed to feed my population. I have no surplus, so my city cannot grow. However, the benefit is that my Warrior will be produced 3 times as fast as before. Notice that it only takes 5 turns instead of the previous 15.
By working the forested grasslands tile, my city produces a total of 4 food, 2 production, and 1 commerce from tiles. My city is once again growing because I have a surplus of food, but my warrior is going to take 8 turns to build now (15 / 2 = 7.5, rounded up to 8).
I'm going to switch it back to the oasis tile. This early in the game I just want my population to grow as fast as possible, and this tile provides more food than any other (3

). I get an additional 3 commerce as well which, as explained before, can be converted to research or gold depending on the settings I choose for my empire.
To try and simplify the commerce learning curve a bit, you can think of commerce as funding for different government departments. You get to decide at all times just how much of that funding goes to each department. Imagine the 4 departments are as follows:
Department of Science (research)
Department of Finance (gold)
Department of Arts & Entertainment (culture)
Department of Foreign Affairs (espionage)
I might choose the following distribution scheme:
40% commerce - Department of Science
30% commerce - Department of Finance
10% commerce - Department of Arts & Entertainment
20% commerce - Department of Foreign Affairs
If my empire generates a total of 100 commerce, that means I have 100 "units" of funding distributed as described above (40 research, 30 gold, 10 culture, 20 espionage points). You can use the little +/- icons next to those icons in the upper left to change the distribution empire-wide. Note that you can't change this distribution on a city-by-city basis - it always affects all the cities in your empire the same way.
Going back to our game as an example, notice that I am producing 12 commerce total, as shown by the following image (you can see the summary box I have in the upper left by hovering over the numbers for research or gold):
If I am only producing 4 commerce from my tiles, where is the other 8 commerce coming from? Notice that this city has a building in it - the Palace (listed in the left side of the screen under
Buildings). The Palace has the benefit of producing 8 commerce for the city all by itself. Ahhhhh, so that's where the other 8 commerce is coming from.
I have my commerce "funding distribution" set to 100% research, and 0% gold. That means every single point of commerce is being routed to our Department of Science to research new technologies. You can see a mathematical summary of this ratio by hovering the mouse over the number next to the beaker. My base commerce from the city is 12, and 100% of 12 = 12, so my city is producing a total of 12 research.
What happens if we change the ratio in the upper left using the +/- buttons? Let's try it! Let's move research down to 50%.
Notice that I am now producing 6 research and 6 gold. 12 * 50% = 6, so that makes sense. You can play around with this to see the effect, but for now I am going back to 100% research. I don't have any particular need for money in my treasury right now, but I do want those technologies faster, so it makes more sense to stay at 100%.
Ok, now that we've dug into the guts of city management and gotten a basic understanding of how food, production, and commerce work as well as how to force population to work specific tiles, we are official done the first turn. Don't expect every turn in the game to have a huge post like this. I just wanted to make sure I explained this finer point of managing a city (in particular, commerce) so that future decisions make more sense. Please let me know if you have any questions on this topic. I'll try to post the remaining 15 turns tomorrow night if possible, but no guarantees as I am flying to San Francisco.
I hope you are enjoying Civ 4 Dummies so far. Until next post!
