What's new in Team Fortress 2?
To start a trade just go to backpack and select the "Trade" icon at the bottom. Then select a player from desired list (friends list, players on server or Steam ID). The other player will have to accept your request to proceed further...
Your backpack (left half of the screen) will show up. There will be some box on the TOP RIGHT for what YOU want to trade and at the bottom right for the person you previously invited.
Just put what you want to trade in the appropriate boxes and click the "Ready to Trade" checkbox. If the other player have clicked the checkbox too, the "Trade Now" button will be highlighted. Click this to proceed the trade!
Thats it you're done!
Don't trade special or valuable items with unknown players... Some people can offer you the moon and as you check "Ready to trade" they remove what they putted in the trade, quickly check the box "Ready..." and as fast as they can, they click the "Trade Now" Button. You'll end up with trading 3 hats for a grenade luncher... This is not funny... There is several other ways to get caught... If you suspect something than... DON'T TRADE... It's all that simple and the other player is probably somewhere else around the country or even farther on the globe...