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.
It doesn't work for me, which is pretty annoying to be honest - I didn't try it on the laptop yet, hope that it'll work out then.. All I see is the topic :$