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.
In my opinion you should try bloxburg, mad city and simulator games. I rate roblox 8/10, and it is because of the robux system that makes it pay to win.