Each user controls the sharing of their own calendar.  Follow the below steps to share your calendar or send these steps to the person who owns the calendar that you need to access.

 You can also share your own calendar for others to see or delegate access for others to edit it.

Share a calendar with others in New Outlook for Windows

Create a step-by-step guide

1. From the navigation pane, select Calendar.
2. On the Home tab, select Share calendar, and if you have more than one calendar, select which calendar you want to share.
3. Type whom to share with in the Enter an email address or contact name box. If the person's name appears in a list, select it, otherwise press Enter.
4. After you’ve added the person you want to manage your calendar, select the drop-down list next to their name, and choose the level of access you want them to have.
   • Select Can view when I'm busy to give them permission to see only when you are busy, but not the details of items on your calendar.
   • Select Can view titles and locations to give them permission to see when you're busy, plus the titles and locations of items on your calendar.
   • Select Can view all details to give them permission to see all details of items on your calendar. others to view your calendar but not make changes to it.
   • Select Can edit to give them permission to make changes to your calendar.
   • Select Delegate to give them the same permission as an editor, plus they will receive meeting requests and responses on your behalf. To allow the delegate to see events on your calendar you marked Private, select the check box for Let delegate view private events. 
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Note: for details about delegate options, visit Outlook Calendar Delegate Options.

5. After you’ve finished adding the person you want to share your calendar with and have chosen which permission you want to give them, select Share. If you decide not to share your calendar right now, select  Remove.
6. The person you're sharing a calendar with will receive an email invitation to share their calendar. Once they accept, they can add your calendar to their own view.