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 made 2 new different accounts where I made my first mission but in both cases they rejected my proof saying it's not a new register account (spoiler alert: they were new). This guys don't really feel like giving you the money for completing the tasks. Nice.