Add a shared Office 365 calendar in Outlook for Windows (Office 365 Client)

Open Microsoft Outlook
At the bottom of the navigation pane, click the calendar icon
On the toolbar, click Add Calendar
Select Open Shared Calendar...
In the search field type in the name of the calendar you wish to add
Select the calendar from the search results and click Ok
Within a minute or two, the calendar will appear in the Shared Calendar section on the left