you mean steam CD keys? They are games you can activate on steam. If you want to register them you can go to steam, click on "add a game" next, click "activate a product on steam" and then paste the product code gamehag gave you.
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in 3 steps
Choose the game that interests you and play itfor free.
Every game has some quests for which you will receive Soul Gems.
You can exchange your Soul Gems for Steam Wallet top-ups, game keys, CS:GO Skins and other rewards.
You know that on Gamehag you can get real rewards for free, right? Join us, complete walkthrough and get your chest!
What are keys and how do you use them when you get them?