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.
You can exchange your Soul Gems for Steam Wallet top-ups, game keys, CS:GO Skins and other rewards.
Do not use the same gaming account for Crossout as you did with i.e. War Thunder. Your tasks will be rejected. Basic f*cking information not clearly shown by gamehag. Time wasted. They won't even say that you need a different account when they reject your screenshots. I had to go through the "contact" to get the information.