Buy Death Squared

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 Nintendo's download platform. After buying a Nintendo Switch game, you will receive a download code. Start the Nintendo eShop from the Home menu, select Settings/Other, and then tap "Redeem Download Code" to enter your 16-diogits code which will allow you to download your game.