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Classic Outlook
In Calendar , click the Home tab.
At the top menu, click Add Calendar > Open Shared Calendar.
Type a name in the Name box, or click Name to select a name from the Address Book.
The shared Calendar appears next to any calendar that is already in the view.
After you access a shared Calendar for the first time, the Calendar is added to the folder pane. The next time that you want to view the shared Calendar, you can click it in the Folder Pane.
New Outlook
In Calendar, click the Home tab.
Click Add Calendar - It is positioned above all the calendars.
In Add from directory tab, enter the name or the email address to search.
Select an Add to option and click Save
To delete a calendar, click the three dots next to it and select Remove.