As an avid user of Outlook, you most likely pop back and forth between the calendar and the inbox. There are a 2 ways you can view both your calendar and your inbox at the same time. If you have multiple monitors, the first method is great - it gives you a full view of each window whereas the 2nd method is great for a smaller view of the calendar and if you only want it on a single screen.
It's pretty standard that most people have multiple screens and there's an easy way in Outlook to have your inbox and calendar open in their own separate windows, one on each monitor. You can use this method with Inbox, Calendar, People, Folders, Tasks and Notes.
Alternatively, you can also change your single screen display to view your mini calendar. This is a smaller view of the calendar but does let you see some of the immediate upcoming things on the calendar.