NOTE: Please follow these steps from the Calendar's Owner Account.
Step 1: Go to Outlook Web (https://outlook.office.com/mail/inbox)
Step 2: Click on the 'Calendar' icon
Step 3: Click on the three dots for the calendar you want to share
Step 4: Click on 'Sharing and permissions'
Step 5: Enter the users you would like to give access to
Step 6: Select the permission you would like the user to have to your calendar
Step 7: Click 'Share'
Step 8: The User you are sharing to will need to accept the invite