In Outlook, select “File” from the menu bar, “Open”, and select “Other User’s Folder…”.
In the “Open Other User’s Folder” dialog that appears, type in the name of the calendar you are adding in the User field, then select “Calendar” for the Type.
If you don’t know the exact name of the calendar, you can click on the Address Book icon () and search for the calendar:
Type in the calendar you are looking for.
Select “Find”.
Select the calendar you are looking for and choose “OK”.
Finally, click “OK”.
The calendar should now appear in your “Shared Calendars” list.