Buy Beyond Good and Evil

For Steam CD Keys, you must download (HERE), install the Steam software and create a new account. If you already have a Steam account, once you log in, click "Add a game" (located in the bottom left corner), and then "Activate a Product on Steam". After a few more clicks, you will be prompted to type in your game code. Thus, the game will be activated and automatically added to your account library.

Uplay is Ubisoft's Download Platform. If you still don't have the client, you can download it HERE, install it, and create a Uplay account if you don't have one already. Then you will have to get the Download Manager related to your game, unzip its content and use the .exe file which will download your game. At last, once the download is over, you just have to get back on Uplay where you will see your games cover and click it to activate your CDKey.

This is the Epic Games launcher. You must download the client HERE, install it, and then create your account. When you sign in to your account, click on your avatar and then on "Redeem Code". Enter your Key, your game will automatically be added to your library, and the download will start.