To share a calendar in Outlook on the web (OWA), you need to:

  1. Open a calendar that you want to share with other users in your Office 365 organization. You can access it from the main menu in Outlook on the web (you might need to click All apps to see the Calendar option):
    Calendar appor by clicking the calendar icon at the bottom of the left pane:Calendar icon in Outlook
  2. From the My calendars list, select a calendar you want to share.
    My calendars
  3. When you hover over the chosen calendar, three dots will show up next to its name. Click the dots and then Sharing and permissions.
    Sharing and permissions
  4. Now, you can select individuals you want to share the calendar with. You need to add them one by one.
    Select people to your share calendar with
  5. You can set up access rights for each person separately. This way you decide what people can do with your shared calendar. To confirm the setup and start sharing the calendar, click Share.
    Access settings
  6. The selected person will show up on the list below. At any time, you can change the access rights for a selected person or remove them from the sharing list by clicking the trash bin icon.
    List of users with calendar access
  7. Once you click the Share button, the person you specified receives an email where they can accept your calendar sharing invitation by clicking the Add this calendar button.
    Accept sharing invitation
  8. After that, the email recipient can view the shared calendar by clicking the View calendar button.
    View calendar
  9. When they go the Calendar view, the shared calendar should be displayed there along with their other calendars.
    View a shared calendar

Kind Regards,

Matt