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.
What do you say on league on mobile ? Do you think it's going to be good ? I think it's going to be not that bad, cuz the matches are going to be much shorter and some animations looks much better than in original game :).