The owner of the calendar must give permission to view their calendar. If an invitation has been sent by the person who wishes to share the calendar, accept it. You will now have access to that calendar under the Shared Calendars heading.

To add a calendar manually:

• Open Outlook.
• Enter Calendar mode.
• On the Home tab click Add Calendar and select From Address Book...
• Browse for names or type them in the Search box.
• Double click the name required and click OK.
• The calendar has been added under the Shared Calendars heading.