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.
I only played the game for the reward but i actually really got into it after a while. My favorite playing modes are the Aircraft and Tank fields. In other words, its really fun to play.