A Nintendo Switch gift card is a way to pay for games and downloadable content in the Nintendo eShop. It works like a traditional gift card, but instead of cash, the card contains a code that can be redeemed to add funds to your Nintendo Switch account.
Once you purchase a Nintendo Switch card, you enter the code in the "Add Funds" section of the Nintendo eShop. Once the code is redeemed, the funds are added to your user account and you can now use them to purchase games, subscriptions, and downloadable content.
To redeem your Nintendo gift card you must enter the card code in the Nintendo eShop and the balance will be automatically added to your account.
Once funds are added to your account, simply search for the product you are interested in and purchase it with your account balance. Since the card was purchased at a discount, the game will be cheaper!