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 an account and played the game even exceeding the requirements by just a bit and it said new account wasn't registered. I used the link and did everything, same username and all but got denied anyway.