When a colleague shares a calendar with you, it needs to be added to your calendar.
Step 1: Open Microsoft Outlook
Step 2: In the bottom left corner of the screen, click the Calendar icon.
Step 3: Click Open Shared Calendar
Step 4: Enter the initials of the person that has shared the calendar with you, click their name and click open.
Step 5: The shared calendar will be displayed on the left hand side of the screen. You can choose to display your own calendar and the shared calendar at the same time or by ticking the boxes you can choose any combination you require.