Scroll down for "New" Outlook/Outlook Web.
Outlook Classic:
Go to the calendar tab. This is most likely in the top left-hand corner of your screen.
Right click on the personal calendar you would like to share, then click "Sharing Permissions".
In the menu that opens, click "add."
Search for the name of the person you would like to add to your inbox. Select their profile, click the "Add" button, and then click "OK".
You may adjust the level of permissions someone has in your shared calendar by changing your selection in this menu:
New Outlook/Web Outlook:
Go to the calendar tab in the top left-hand corner of your screen.
On the calendars you would like to share, click on the three dots to open the side menu, then click "Sharing and Permissions."
Type the name or email address of the person you would like to add into the box, then select the correct person from the menu that appears. Use the drop-down menu to select the level of permissions you would like this person to have over your calendar, then click the "Share" button to share your calendar.