When you open an Office program or when you sign in at Office.com, you might see a sign-in dialog box, where you enter your email address.
When you type your email address and click Next, you’ll proceed to a sign-in page where you enter the password that goes with the address you typed.
Note: You might have more than one Microsoft account. Make sure that you sign in with the Microsoft account that's associated with your Office subscription.
Work or school account
The work or school account is what you use to access your organization’s Office 365 homepage.
Check out Where to sign in to Office 365 for more more details about signing in to Office 365.