Buy SteamWorld Dig 2

You need to use your your game CD Key on the Playstation Network to download your game. To access the Playstation Network, you need a Playstation 4, a broadband connexion, a PSN account, and a storage device according to your console: Hard disk drive, memory card, or USB drive.
Playstation Plus Subscriptions are compatible with PS4, PS3 and PS VITA.

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.

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.