Trading is the basic method of exchanging items and money and the only way to make gifts. But remember - there's a big difference between making gifts/helping your friends and fully promoting newbies.
To start trading, select a person you wish to trade with and use Initiate a Trade skill (found in Basic Skills)
If he/she accepts your trade request, you can put items/money you wish to trade in the left box. To put some money in, click on any currency symbol (marked with a red frame).
If you're ready to exchange, click the Lock button. When your partner does it too, the trade will be done, unless someone doesn't have enough empty bag slots.
Other trading methods
You can trade with all players at the same time. To start vending, use Vend skill (found in Basic Skills)
The upper box is for items you want to sell. Drag some goods here from your bag and enter the price. In the lower box you can drag items you want to buy. Keep in mind that not everyone will buy at the prices you type. Check Trade Realm or Auction House for current prices.
The next important thing is your stall name. Choose it wisely, your potential clients like to know what they can buy or sell. The name can contain only 13 characters, sometimes it isn't enough, in this case you can write for example: WTB/WTS.
Vending takes a lot of time. If you want to sell or buy quickly and then go, the Auction House is the perfect solution. There all the offers are taken by players from all 10 realms across the servewr. It's an easy way to find items you want and check the worth of your stuff. Each of your auctions cost some Soul Coins to post. After a successful sale, your profits are lowered by a fee (2% of the total profit). Due to this money loss, rare and expensive items are often traded through the World Chat.