trade is civ3

[Devil's Advocate]

How do I get trade routes started?

Im new to this game and I dont understand how to trade stuff. Do I have to get to a certain point in history?

[notyoueither]

You trade resources and luxeries with other civs in diplomacy.

If you are on the same land mass you will need road connections with the civ. You can use roads through a 3rd civ if you are not at war with the 3rd civ.

You can trade through Coastal, Sea, and Ocean tiles once you have the required techs. To trade over water you and the other party of the trade both need a harbour (or airport) in your trade network (connected by road to your capital).

[Willem]

You also have to make the deals in your Foreign Advisor screen, F4, once you have a road/harbour/airport connection with them. If you begin to deal with them, you'll see a list on either side of what can be on the table. If the Luxuries/Resources are greyed out, then you don't have a connection with that civ.

[Spiffor]

You must have resources (a road on a resource tile within your borders connected to your capital), and your capital must be connected with someone else's.
To trade across sea, you'll need harbours (in one of your connected cities and in one of their connected cities), and must be separated only by coast until you discover astronomy, and must be separated by no deeper than sea until discovering magnetism. When you discovered magnetism, every harbour is automatically connected to each other.
When you have resources and are connected with foreign civs (by pressing F2, you know with whom you can trade, and which cities are not connected), go talk with someone, and click "luxuries" or "resources" ; then click the thing you want to trade and give the price. Notice you won't see here the resource you want to trade if they already have it : they don't need more than one.
Voilà ! You can now trade with a foreign civ !

[Autolicus]

Oh, for God's sake, read the manual.