Open Outlook on your Mac

Click on the Calendar icon

To the right of Shared Calendars you will see three dots (you may have to hover it).  Click the three dots.

Choose Add Shared Calendar

At the Open Calendar dialog box, start typing the name of the person or email address of the calendar you have permission to view in the search bar.  When you see the calendar you want, click on it to highlight it and click on the Open button.

Once it validates that you have the correct permissions it will be added to your Shared Calendar list.