Steam's trading card system automatically deposits trading cards into your inventory on a time-release basis. For Airport Madness, you get one every 30 minutes. Steam manages trading cards for all games in the same manner. You only receive half of a game's cards (our game has 8) from just playing the game. The rest are obtained by trading with other players in the marketplace. Once you have an entire collection of cards, you will earn "badges". Good time-wastin' fun!
