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.
Some chests have really awesome game keys in there, but along with that are runes. And apperently, these runes ain't worth the chest's price at all, and I'm pretty sure that's all you'll get from them. Can't you just remove the runes from the chests? For example, I want Overwatch from a chest, and any other game in that chest, I either already have or don't want. My chances of getting something EXCEPT Overwatch are really high. What I'm saying, is the chests are random, so if you're not happy with your prize, then too bad. That's okay, but at least put in stuff that's worth the SG we pay, because now it's just a big scam.