Steam Trading cards

Check here for the Trading Cards FAQ

Games in your library will drop a limited number of cards, usually a number of cards that equals half a set. If the set of a game is made of 6 cards, your game will drop 3. You will have to acquire the rest of the set by trading with others or by buying the remaining cards on the community market.

Once you have a full set of cards, you can head to your "badges" section and craft a badge. Crafting a badge will delete the cards and a badge will appear on your profile. Your "level" will also be increased.

Once one of your games has dropped all its cards, it's over. There is, however, a chance that you will someday have a "booster pack" appear in your inventory. Booster packs will contain 3 random cards of the game you got all the cards from.

You can either sell your cards on the market for Steam Wallet money or use them to trade and craft badges.

Increasing your level at least to level 5 will allow you to vote on community-voted sales during Steam sales. At least that's how it was in the past.

The higher your Steam level, the higher the chance you have to have a booster pack appear in your inventory each time a random user, somewhere, crafts a badge.