How do you claim a steam key/code?

Once you've gathered enough Buffs, head over to the marketplace (that's the little trolley) and find yourself a steam card (You can get them on Amazon too if they're sold out.) once you've claimed it, just head over to steam, and under "Games" you'll find "redeem wallet code." enter your gift card number into the field and you'll be on your way to getting that new game of yours!