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've been hearing a lot about Unturned recently and it seems interesting enough. Problem is, I don't exactly have anyone to play with. I don't suppose either of you or anyone else, know of someone who streams/does let's plays of it?