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.
The 3rd requires 250 topaz and it can only be obtained by cashing the game, it is definitely not worth to spend $4 dollar plus for 500 plus soul gems and its definitely disappointing to me. But overall the first and second stage was indeed easy to complete and enjoy it quite a lot, the only problem was with the 3rd stage.