Xbox Gift Cards are prepaid cards with a pre-determined balance and are used to add funds to your Xbox account. Once funds are added, they can be used to purchase games, Game Pass subscriptions and other products in the Xbox store.
When you purchase an Xbox Card you must log in to your Xbox account and redeem it to add the balance to your wallet.
To redeem your Xbox gift card, log in to your Xbox account and select "Redeem Code". Then enter the card code and click "Redeem". The balance will automatically be added to your Xbox account.
Once you have added the balance to your wallet you can use it to purchase games and Game Pass subscriptions.