This may sound sort of obvious, but in order to manage your boss's calendar (or anybody's), you'll need to see it. To do this, you'd first add the calendar to your list of Other Calendars. You would do that by clicking Open a Shared Calendar in the Calendar Navigation Pane.
You can view the boss's calendar in either of two ways: in your own Outlook window or in a window all by itself. How you choose to view it is purely a matter of your preference. As far as Outlook is concerned, you're the boss.