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.
Long story short, THEY AREN'T. So don't go buying them. It's a **** gamble and it really won't get you anything. The proof is in my inventory you see I got 1 Robux 2 times. Those 2 Robux was from the 350 soul gem chests which I bought twice. Huge regret. Do not go buying them, you will also find more threads about gamehag's chests being a huge scam. This is a big warning, DON'T BUY THEM AND DON'T ACCEPT THE RISK.