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'm willing to trade 4 random codes from my collection, per 500 Soul Gems. If you're interested you can message me for details. As far as I remember, you need to be a certain level, before you can send SG to other users. Please make sure you can actually send the Gems, so we don't waste each other's time.