This week Valve has opened up their new Steam Trading Cards to all Steam users, allowing the new Steam Trading Cards to be collected and traded with other Steam users or traded in for a variety of in game goodies.
Steam Trading Cards are virtual cards earned by playing games on Steam and complete sets of cards can be turned into game badges and tradable Steam community items.
Steam users can play any participating Trading Card games to get trading cards a full list of all supported games is available here. Once you have collected a set of Steam Trading Cards you can craft them into a game badge. Like the current badges, they are tied to your account and are shown on your profile.
However unlike the current badges, crafting game badges earns you marketable items like emoticons, profile backgrounds, and coupons. Level up your badge by collecting the set again and earning more items. Enjoy!
For a full list of Steam Trading Cards FAQs and how they can be used jump over to the Steam website, to answer any questions you might have.