These simple steps show how to add a Microsoft calendar on Mac (Outlook.com, Office 365, Hotmail and Live calendars).
Install OneCalendar
Download OneCalendar from the store and install it on your device.
Select Accounts overview
Select the OneCalendar menu on the top left, and select the option "Accounts".
Select Add account
Click on the "+" sign to add a new account.
Select Account type
Click on the "Microsoft" account type.
Enter credentials