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 am going to be honest with gamehag and its users its a good website but the fact that they make the chest cheaper than what you want is reasonable but you have a .0005 percent chance to get your thing because I have open multiple chest and gotten either 100 soul gems or a random steam CD code worth nothing.