Don't forget to use your Xbox Live account! You can also use your Microsoft/Windows account, too. If you've played a game on any Xbox console or from the Windows Store, you probably already have an Xbox Live account.
Need a step-by-step guide?
https://help.mojang.com/customer/portal/articles/2461010
How to create a new Realm:
https://help.mojang.com/customer/portal/articles/2461089
Have feedback? Go to our official feedback site here & give your feedback to the Realms team.