Open Outlook
Go to Calendar
Select the calendar you want to share
Right-click the calendar
Choose Properties
Go to the Permissions tab
Click Add to add people (or select them from the Address Book)
Select the user(s) you want to share with
Choose a permission level (e.g., Can view when I’m busy, Can view all details, etc.)
Click Apply
Click OK
(For Microsoft 365/Exchange) Send a sharing invitation if prompted
(For Outlook on the web) Open Outlook on the web → Calendar → Share
Select the calendar and enter the recipient’s name or email
Choose permission level
Click Share