How Do I claim my rewards?

Simple, go to google and type in "activate a game or product on steam".Click the steam website and log into your account.After that, it should redirect you to a page that lets you enter a code to get the game.Also, on the official steam app in the bottom left it says the same thing, click it and enter the code in.If you still don't get it contact me via friend request.I will get back to you as soon as I can.
Have a good day!

Actually, to clear this up a little better, Steam released their new "Browser Redeem" feature, so you don't have to have your Steam client open to redeem a Steam game code. I have this piece of javascript bookmarked that I made the other day which makes it a whole lot easier. What it does is open a prompt when you click the bookmark and you paste the code into it and then once you press "Ok" it'll take you to Steam's redeeming page with the code from the prompt pre-entered. Saves you a few seconds.

javascript:void(location.href='https://store.steampowered.com/account/registerkey?key='+prompt("Insert Steam key"))

Just highlight that and drag it to your bookmarks bar and it'll work like a charm.
PS: You need to be signed into the Steam website.