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.
With the resent updates warframe did get more attention I think that it holds a lot of potential to keep up with future titles with a little bit of fine tuning from the developers