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.
You can exchange your Soul Gems for Steam Wallet top-ups, game keys, CS:GO Skins and other rewards.
Can you earn more than just 1 SG at a time by actually downloading the app and doing something or do you only earn 1 per video and thats it?