STEAM CD KEY : Use the Steam Key Code on Steam Platform to download and play Randals Monday. You must login to your Steam Account or create one for free. Download the (Steam Client HERE). Then once you login, click Add a Game (located in the bottom Left corner) -> Activate a Product on Steam. There type in your CD Key and the game will be activated and added to your Steam account game library.
STEAM GIFT : A Steam gift is a one-time transfer you receive. You activate and install Randals Monday to play on Steam, it is a non-refundable game that stays in your Steam games collection. Please read the store description about any language or region restrictions.
GOG.COM CD KEY : You need to register on Gog.com, then use the GOG Key to download and activate your game to play Randals Monday.