His Excellency Aethien wrote:
I still have no idea what those cards are for or how exactly that sh*t works.
That's because you don't understand the metagame
Certain games drop cards that go into your Steam inventory. You can see which games from your Badges page (drop down under Community I think). When you're playing those games, you randomly get a card every once in a while. The cards can be combined for badges to increase your Steam Level and give some minor perks (more showcase slots in your profile for example) and an emoticon & background. More importantly, you can sell them to other people who care more about that **** than you do.
To get cards faster, you can use a program called Steam Achievement Manager. SAM allows you to edit your Steam Achievements but that's not why you want it. You want it because just by bringing up a game in SAM, you make Steam think you're playing it. Plus, since SAM communicates directly with Steam's achievement database, you don't even have to have the game installed. Instead of downloading some 20gb game and letting it idle for 3 hours, you can just pop it up in SAM. You can also have multiple games "running" in SAM at once which you can't do by actually launching them via Steam.
On their own, the cards aren't worth much (usually 10-15¢) but taken in aggregate you can make a nice nest egg for the cost of a few mouse clicks now and then while you're sitting at your computer anyway. And during events like the sale where cards go up in price because people are dumb enough to buy cards to make badges for a 1/500,000 chance at getting a couple free games it's even better.