Xbox Activation Guide

Press the Xbox button on your controller to open the guide, and then select Store
Press the View button on your controller to open the side menu, and then select Redeem
Enter the 25-character code, select Next, and then follow the prompts

Go to redeem.microsoft.com
Sign in to the Microsoft Account associated with your Xbox profile
Enter the 25-character code, select Next, and then follow the prompts

Press the Start button on your keyboard, and then enter Xbox into the search bar
Choose the Xbox app from the results to open the app
Select your gamerpic, and then select Settings
Select Redeem under Redeem a code
Enter the 25-character code, select Next, and then follow the prompts