Most users should already have Microsoft Authenticator on their phone. If you don't, install Microsoft Authenticator from the App Store (iPhone) or Google Play Store (Android):
You will then be prompted to scan a QR code using your Microsoft Authenticator app:
On your phone, open the Microsoft Authenticator App:
On your phone, within the Microsoft Authenticator app, click on the "plus" icon n the top right corner:
Click on "Work or School Account" and then "Scan QR Code":
Use your camera to scan the QR Code displayed in the browser on your computer (You may have to allow the app permissions to the camera).
Now you should see a "WebFMS" account with a 6-digit code anytime you open the app. Enter the 6-digit code into the text box and click "Validate Code".