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.
Not all indie games are bad! If you want someting for free, you need to have in mind that or you gonna watch a lot of ads, or you need to spent a lot of time. In either way, you won't spend your own cash, soo, it's up to the taste. If you just want an AAA games, don't use this sites, but if you don't care at all if it's a B game or an AAA game, than I think it's worth :)