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 seem to have this problem with all Android games where the registration process doesn't ever seem to work therefore you can never complete a quest. Anyone actually get beyond task 1 for this reason?