Step 1: Access the Outlook webmail login page https://outlook.live.com/calendar/0/view/month in a browser.
Step 2: Click Sign in on the top-right corner.
Step 3: Enter the username and password for the account which has the calendar.
Step 4: Now, on the Calendar screen, click Share on the top-right corner.
Step 5: Now, enter the user’s account to whom the Calendar must be shared.
Step 6: Click on Share.