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 don't know about you, but I personally hate this. Everyone was playing "piano" in their phones, I was starting to get sick. But then I realised how better it was than fortnite... I just wish that fortnite ends once and for all, and then I also wish that no other crap-like game becomes popular worldwide ever again