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.
In my opinion, depends on the player, but teams like Munich, Real Madrid, Juventus and Dortmund can beat it pretty easily even though Barcelona is a good team.