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.

Screencap of the "Enter a Passcode" option

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.

Example of the field to enter a passcode

6) Click Log In, and you now have access to the MFA-protected application.