Play games
Choose the game that interests you and play itfor free.
Complete the quests
Every game has some quests for which you will receive Soul Gems.
Receive rewards
You can exchange your Soul Gems for Steam Wallet top-ups, game keys, CS:GO Skins and other rewards.
The game starts nagging you to download a high res texture pack at some point. DON'T DO IT! I figured it would be a hundred MB or maybe a gig or two at most. IT'S 18GB! And it didn't even start downloading until after it did "analyzing files" for 30 minutes. I just wanted to play a couple matches today, but now I'm stuck downloading and there is no way to cancel the texture download once it starts. You can't play until it finishes. So I guess my afternoon is gone and I'll have to find something else to do.
Ps. The game looks just fine without the high res textures. I never even noticed the difference.