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.
It's a pretty good game when you try it out, it's got great graphics, realistic physics and balance, and at first glance it was just for the soul gems, but when I played it was great. Pretty satisfying to see explosions.