Trading
To begin a trade with another player, stand next to the other player and press 'Ctrl+T'.
Now find and press the 
'Trade Icon' and click on the other player.
Drag the items you wish to trade from your inventory to the 'My TradePack' grid, and click the left most red arrow, turning it green. This lets the other player know that you are finished with your offer.
The other player will do the exact same thing and check his arrow as well. Once both of you are ready, you can look over the trade and then click the 
'Confirm Trade Icon'.
It never matters who starts the trade, and you can also trade gold in the same fashion.