Using New Outlook on Windows for personal email, calendar, and contact management
Assuming you are viewing your email, right-click on your Inbox folder and from the context menu choose new window. Now that you have two windows showing your email, just click on the calendar icon in one of those windows and you will have a window with your calendar and another with your email.
As long as you quit Outlook from the Outlook menu then those two windows will reopen when you restart Outlook (at least they did for me). Give it a try...