Personally, I think trading cards are one of the most pointless things added to STEAM. But, some people like them... so, for them, yay. You can gather a certain amount of trading cards from supported games by simply playing them. And, the more you play games in general, the more often you have the ability to gain a booster pack. Once you gather all the cards for a game, you can craft a Badge. Which will increase your Steam Level. (again, IMO, pointless) Problem is, some people take this WAY too seriously. I've had people tell me I'm not a "real gamer" simply because I don't do the badge or Steam Level thing. "That guy doesn't know anything, he's only a level 11"... an honest comment I got as a reply once. Personally, I sell every trading card I get. May be 7 cents, may be 50 cents. But, due to idiots manipulating the system... Steam have modified selling items to try and "safeguard" it. Now, you have to use Steam Guard Mobile Authenticator. Which only works if you have a mobile device. Which, believe it or not, there are people... like me... who don't. I hate phones. Absolutely despise them. And I refuse to get one. So, to sell anything now... it has to sit in pending for two weeks before being listed. Which normally means the price I put it up at has now dropped and the item won't sell anymore.