Trading
Trading is a major element of Illyriad. It is unlikely that you will be able to produce everything you need or want, and you certainly won't be able to do so in a timely fashion.

To trade you will need:

• Top four rows of Trade Research Tree.
  
• Guilds->Merchant's Guilds->Faction Markets->Trader
  
• Trade Office->Procurement->Selling
  
• A trader in a hub for Hub trading. It takes 7 days to train.
  
• Caravans. Lots of them.

Two types of trading
City trading
Buy and sell things from your town. It's slow, reliant on your own caravans, and generally awkward. If you can't do hub trading you're better off just asking for stuff. It's all-round easier.

Hub trading
Once you've got the bits of research done and your trader built you're going to want to move your trader to a specific hub. Centrum is the most well known, but you'll also want one nearby to store your stuff. Nothing in a hub can be stolen, so it's very useful to keep things secured.

Buy and Sell orders are handled through the market. More information (past prices etc) is available with the appropriate research. Limited to certain number of buy and sell orders dependent on research and level of trade office or offices in that specific town.

What to sell or buy?
Anything really. Saddles, Cows, hides and animal parts sell well though, especially if you are near elementals.

Mostly though trading is to obtain goods you can't get either at all or quickly enough, and securing your goods in hubs. You can make way more money far more easily by selling terraforms through an alt account.