Sign in with your Microsoft account, or work or school account

For the best experience at Microsoft365.com, sign in with the same Microsoft account, or work or school account you use with Office or Microsoft 365. 

• Microsoft account    This is the email address you use to sign in to Microsoft services like Microsoft365.com or even Xbox Live. It’s called your Microsoft account, but it doesn’t need to be a Microsoft email address; it’s whatever email address you want to use—the same way you sign in to any number of services on the web, like Facebook or Twitter.

• Work or school account    This is the account you were assigned by someone at your organization and what you sign in with to access the various Microsoft 365 services offered by your organization.

After signing in, store any documents, spreadsheets, presentations, and notebooks you create in the Microsoft 365 for the web programs in your OneDrive library. You can then share your Microsoft 365 files via a link and work on them with other people in real-time. This collaboration feature allows you to work together at the same time and see each other’s changes immediately.

Reference URL: https://support.microsoft.com/en-us/office/get-started-at-microsoft365-com-91a4ec74-67fe-4a84-a268-f6bdf3da1804