After your admin has added you as a member of shared mailbox, close and then restart Outlook. The shared calendar associated with the shared mailbox is automatically added to your Calendars list.
In Outlook go to calendar view, and choose the shared mailbox.
When you enter appointments, everyone who is a member of the shared mailbox will be able to see them.
Any member of the shared mailbox can create, view, and manage appointments on the calendar, just like they would their personal appointments. Everyone who is a member of shared mailbox can see their changes to the shared calendar.