A video explanation is also available here.
1) On your computer, go here: https://duo-mgmt.identity.ucsb.edu.
2) Type your UCSBNetID and password in the boxes marked UCSBnetID and Password, respectively.
3) A second screen will appear. Select your smartphone from the Device list first, then click: Enter a Passcode.
4) Now pick up your phone. In the Duo Mobile app, click on the Show link or downward-facing arrow to the right of the tile marked UCSB to generate a passcode.
5) Return to your computer and type in the passcode from the Duo Mobile app into the field next to the Log In button.
6) Click Log In, and you now have access to the MFA-protected application.