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've been looking around both the website and game to come to conclusion that i was not able to find it, if anyone has happened to can you maybe tell me how you did it?