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.
There's so many games to choose from and complete tasks for, so I don't know if I should complete the ones that take a long time and reward a lot or the ones that take a short time and doesn't reward that much