One thing I guess I should mention here is that the Civ3 map is actually a square grid; it's just that each tile is a parallelogram and not a square. If you tilt the tiles in your head, you'll see that the map actually does form a square. This is important because moving directly east or west (using the "4" or "6" key) is actually moving a further distance than moving in one of the other directions. Specifically, a city built two tiles directly east from the capital is actually a further distance away than one built two tiles northeast (think about it). This isn't really a big deal, but it does factor into corruption caused by distance from the capital, so be aware of it.

OK, what are the basic terrain types and what do they do? It's important to know something about what they are and what they do so that you can place your cities in good spots on the map. You can right-click on a tile at any point in time to find out information about it; this is most useful when trying to determine if a tile is on a river or not (if it is, it will have +1 gold listed).

Tundra: Tundra appears near the poles of each map. If you set the map conditions to be cool there will be a lot of it, and almost none if the map is hot. The default numbers from tundra are 1 food, 0 shields, 0 gold. Tundra is an almost useless terrain type because it can never be irrigated to increase its food output. In fact, the only thing you can do with tundra is plant a forest on it to increase shields, or mine it to do the same thing. The only reason to found cities in tundra is to claim it in the hopes of oil popping up there.

Jungle: This terrain is completely useless until your workers get their hands on it. Jungle tiles produce 1 food, 0 shields, and 0 gold. You will get a lot of jungle tiles on hot and wet maps. Once your workers clear out the jungle, these tiles because useful grasslands ones but be warned it takes a VERY long time to cut down jungles. The only real reason to claim jungle tiles is in the hopes of rubber appearing there.

Floodplains: This is an unusual tile produced when a river flows through a desert; the desert tiles that border the river are considered floodplains. You will also see these most often when the map conditions are hot and wet. The base numbers for floodplains tiles are 3 food, 0 shields, and 1 gold (because floodplains are always tiles on a river). Floodplains are great tiles for you to put your early cities near, since when irrigated they provide no fewer than 4 food (3 even under despotism). Use cities on these to pump out settlers or workers like there's no tomorrow. If a city has 3 or 4 floodplains and a bunch of hills nearby as well, you can expect it to be one of your best cities in the future. Cities built on floodplains can be struck by disease though, so be aware.

Plains: This is one of the two most basic tiles in the game, along with grasslands. Plains are an excellent tile that can be used for multiple purposes, and they tend to appear on hot and arid maps the most. The starting numbers for plains tiles are 1 food, 1 shield, and 0 gold. Plains tiles can be either irrigated OR mined though, which allows the player to configure them as desired. In low food regions, plains can produce two food just like grasslands (3 food with railroads). In a high food area, plains can be mined to produce 2 shields and serve as mini-hills (again, mined plains will produce 3 shields with the addition of rails). I tend to reconfigure plains tiles as the needs of the game dictate, sometimes changing the tiles back and forth again with workers as my goals shift. The only time that plains tiles are really bad is if you can't irrigate them.

Grasslands: This is the other basic terrain type in the game along with plains. Whereas plains are 1 food and 1 shield tiles, grasslands provide 2 food, 0 shields, and 0 gold. There are also grasslands with a shield on them scattered around the map; these are known as bonus grasslands and provide 2 food, 1 shield, and 0 gold. Bonus grassland tiles are among the best in the game, and they provide a big boost early on in despotism. Like plains tiles, you can both irrigate or mine grassland tiles. Be warned though that under despotism, you will NOT get a food bonus from irrigating grasslands. My general rule is to mine bonus grasslands and irrigate normal ones, but the great thing about grasslands is that they can be configured to whatever the city using them needs. Grasslands are excellent tiles that normally form the bulk of your territory.

Hills: This terrain type is another one that you want to see near your cities. Hills provide 1 food, 1 shield, and 0 gold, but unlike other terrain types they produce 2 extra shields from being mined. Hills cannot be irrigated, by the way. It breaks down rather simply; if floodplains are your best food-producing tiles, hills are your best shield-producing ones. The best cities are ones that have a mix of both food producing tiles and shield producing ones. Hills also contain lots of nice strategic resources, like iron, horses, coal, etc. You will see more hills on a younger (3 billion years) world. Be warned that it takes a long time to mine and road hills though.

Mountains: Everything that has been said about hills goes for mountains as well, only more so. Mountains are essentially hills that produce no food (they are 0 food, 1 shield, 0 gold that go to 3 shields when mined). Mountains also cannot be irrigated. You should use mountains as your shield-producing tiles, but be warned it takes even longer to mine mountains than it does hills. Still, there are a lot of resources that appear in mountains, and if they aren't quite as good as hills, they are useful tiles in the right situation.

Coast, Sea, Ocean: These are the water tiles, and yes your cities can use them as well! Coastal tiles are 1 food, 0 shields, and 2 gold while sea tiles are the same with only 1 gold and ocean tiles produce only 1 food. All of these tiles can be increased to 2 food by building a harbor in the city in question though. The these tiles are the top gold-producers out there (not counting bonus/lux/resource tiles), so it's a good idea to put cities on the coast that are designed to do nothing except bring in money from the water tiles. It's common to call these "fishing towns", and they can really provide a lot of money over the course of a game. Don't overlook the water tiles when planning where to put your cities!

Desert: This is a tile that isn't very desirable, but you can still use with some work. Deserts are plains without the food benefit; they are 0 food, 1 shield, 0 gold. Not very promising, but of course you should still grab them in the event that oil or saltpeter pops up there later in the game. Deserts can be irrgated to provide one food, and with railroads can actually manage 2 food, though this usually comes late in the game. Deserts can also be mined to get 2 shields, or 3 with railroads, to form a weaker form of the mountain tile. Deserts are essentially a poor man's plains tile, but you can still make them halfway usable with your workers.

Forests: Forests aren't really a tile at all, since they just occur over another basic tile type, but they deserve mention here nonethless. Forests provide 1 food, 2 shields, and 0 gold, but they cannot be irrigated or mined, and they therefore get no benefit from rails. As a result, forests are excellent tiles early in the game, but become useless once rails are discovered. They can also be cut down to provide a one-time bonus of 10 shields to the city they are in the 21-tile radius of. Generally speaking, use forests when under despotism and when most of the land is unworked, but as you progress through the game you should cut them down and improve the basic tile under them (plains or grassland) to your liking.

Whew! That was a lot of text. Since that took up so much space, I'll try to be less verbose when going over the special tiles. These fall into three categories: bonus resources, luxury resources, and strategic resources. All of these are important, but strategic resources are the most important so I will give them the most space.

Bonus Resources: These are special tiles that don't provide any happiness or unit-building effects, but instead produce more food, shields, or gold from that particular tile. The best bonus resource is undoubtably cattle, which add 2 food and 1 shield to the terrain it appears on (either plains or grassland). There is NO better starting position than on a river with a cattle in range. Irrigate a cattle and you're well on your way to being able to pump settlers out like no tomorrow. Almost as good as a cattle resource is a wheat one, which adds 2 food to the default tile. Wheat resources can appear on plains, grasslands, or floodplains; a floodplains wheat produces 4 food even under despotism, 5 when irrigated, and 7 when railed and irrigated out of despotism. These are the best tiles because they increase food, which is always the limiting factor in early expansion. Game resources are probably the next best; they add 1 food but only appear in forests so are not that great. Fish and whale tiles appear only in water tiles and can give a major boost to towns founded on the water. Finally, gold tiles add +4 gold to either a mountain or hill; not real important, but nice anyway. It's important to plan your cities around these bonus resources and to take advantage of cattle/wheat ones in the early stages of the game simply because they can speed up your expansion so much.

Luxury Resources: There actually isn't much to say about luxury resources; they each provide one happy face in each of your cities that are connected to the luxury. In order to be connected, each city needs to have either a road to the capital, a sea route to the capital (or to another city connected to the capital) through the use of harbors, or an air route through the use of airports. Having luxuries hooked up is pretty much a necessity if you're going to play on Emperor/Deity where you only get 1 content person in each city. I should also mention that a marketplace in a city provides more happiness for each luxury above 2 you have present there; specifically, a marketplace provides one extra happiness for having 3-4 luxuries, 2 extra happiness for 5-6 luxuries, and 3 extra happiness for having 7-8 luxuries. Maybe I should sum this up better:
With Marketplace: 1 lux = 1 happy face. 2 lux = 2 happy faces. 3 lux = 4 happy faces. 4 lux = 6 happy faces. 5 lux = 9 happy faces. 6 lux = 12 happy faces.
7 lux = 16 happy faces. 8 lux = 20 happy faces.
Is that easier to understand? You can see how having all 8 luxuries with a marketplace provides a huge bonus, although getting all 8 can be difficult. The luxuries themselves are largely the same, except for a few little differences. Wines provide an extra food for the tile they are on, furs produce an extra shield, and gems and silks produce the most gold (+4 and +3 gold, respectively). Luxuries never move and can be traded over and over again throughout the game. Secure them as soon as possible!

Strategic Resources: These are the meat of Civ3's resource system; some like them and some hate them but regardless of what you think, you need to be aware of what these are and what they do to use them best. Like luxuries, strategic resources need to be connected to your cities for them to have any effect; if you want to build swordsmen, you need to have the cities building them connected to iron. I'll try to go through them one by one and describe each one in a few words. Iron is the most important early resource; you're in trouble if you can't get your hands on some iron in the early game. Iron is needed to build key units like swords, pikes, and knights. Also note that iron is needed to build railroads along with coal in the industrial age. Iron tends to disappear at a rather high rate, so try to secure multiple sources if at all possible. Horses are an important resource, but not as necessary as iron. If you want to build a unit that moves fast before the industrial age, it's going to require horses. Horses and rubber are the only two resources that never move, by the way. Saltpeter is the only middle ages resource, and it's needed to build muskets and cavalry. Not as important as iron, but you still want to have one. Coal is another resource you have to have, because it's needed to build rails. There are no key units that require coal to build though, so if you think you can survive without rails there's no other need to acquire it. Rubber and oil are both absolutely necessary resources, as important as iron in the ancient age. Without rubber, you can't build infantry or any kind of wheeled vehicle (like tanks, mechanized infantry, etc.) Oil is needed to build tanks and any kind of modern ship or plane. In the modern age you need to get your hands on aluminum to build modern armor and spaceship parts, but you can ignore it if going for a diplomatic victory. Uranium is not very useful at all, but one spaceship part requires it so you will need it at some point if you plan to launch the ship. Uranium moves more so than any other resource though, so don't count on your staying in place for long. One final note: the AI civs can always see all of the resources on the map, even ones they don't have the techs for. If you see an AI settler founding a city in the middle of a huge desert, or out in the far reaches of the tundra, you can bet a strategic resource is going to appear there later in the game. There's little you can do about this, but be aware of it and make it a priority to capture these sites when fighting a war.

That concludes this section; the next one will address units in great detail.