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.
How come I can't get Algiz and Raido runes anymore? I just now noticed :P. They're not in any chests that I can find, and the reward part for them says that they're out of stock. How long have they been out of stock for? I only joined a few weeks ago, so I don't know.