Using Microsoft Authenticator App (iOS & Android)
You will be prompted to authenticate your sign in every 7 days and when you sign in to a new device. For example, when you login to Outlook on your computer, it will provide you with a randomly generated two-digit code shown below:
Then it will send you a notification on your phone to allow the sign in. Click on the notification...
It then will prompt you to enter the two-digit code as shown below...
Please note: If you're authenticating the sign in on the same device you have the authenticator app installed, it will only show the two digit number for a second then block it to enter it. However, you can click on "I can't see the number" in the screenshot shown below and it will disappear for 3 seconds for you to see the number then reappear again to enter it.
What to Expect/How Many Times Do I Need To Authenticate
MFA will ask you to authenticate once a week when using installed apps such as Word/Excel/PowerPoint on the same device. It will ask you to authenticate on other devices you use or to a new device you never used before.
-Teams app and Outlook app can be separate authentications once a week also.
Therefore, it can be up to three authentications once a week. You would know that Outlook or Word apps need to be authenticated when you see an exclamation mark next to your name on the top-right of the app.
-For office365 activity in a web browser, it will ask you to authenticate every time you sign in to a web browser because browsers don't hold token keys. If you login to the browser often, checking the following on the login screen may help. (ensure the box is ticked and click yes. It doesn't work in incognito)
-If Teams need to be authenticated, it may miss calls unless it is authenticated only once a week on the same device for the locally installed teams app.