Not much has changed since the beta, other than it being more widely available now. Steam has an FAQ explaining all the details of how to trade. Essentially you can only trade with friends and those in group chat by clicking on them. You can view your inventory of items on steam now and not just in game.
This looks pretty cool. Being able to swap items that you don't want or use with friends in exchange for games seems like something that could catch on. we could end up with an entire marketplace where people are swapping games and items. Will be interesting to see how this unfolds.