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 never tried to go deep into games history except for Warframe. Does well known games begins like this game or like League of legends 4 ? I really do not understand how people play this type of games !