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.
Ref (you get 200 if the person reaches 1000) and codes (gives you chests, you can liquidate that into SG), by creating news and videos (but amount varies)