Shared calendars in Apple Calendar

Make your calendar available to others

Go to Preferences → Accounts → Exchange → Delegation. Click the Edit... button to change who should have access to your account (your calendars and tasks). In the window that pops up, press the Plus (+) button. Enter the name of who you want to give access and then set the level of access: No Access, Read Only, Read & Create or Read & Write.

See the calendars of others

Ask them to share their calendar with you. See above for how to do this on a Mac. When the person has shared the calendar, go to  Preferences → Accounts → Exchange → Delegation.

Click the Plus button (+), and enter the user's name. Here you will see what kind of permissions you have in their account (here:  read permissions to calendars, no permissions for tasks).

To see the account's (user's) calendars in Calendar, activate the option Show on the left.

You can turn off the display of others' calendars in the left column under Delegates.