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 found the Roblox Contract really easy to do as it didn't take me too long to complete all 3 tasks and the game was enjoyable. I would recommend playing this game and getting your friends to tag along with you too.