Hi Makarita,
We use this email address as your Office 365 account. You can sign in to Office 365 portal with this account to manage Office 365 settings and related features. Also this address can be used for email service.
You can refer to Office 365 for professionals and small businesses: A tour for administrators to know more about what we can do with Office 365.
Thanks for your understanding.
Thanks,
James Yao