Calendar is too busy/confusing when all three sections appear at the same time.
You can toggle courses off from the side-bar menu on the calendar tab.
The Calendar spans all courses and displays information for each of your enrolled courses and groups. In the navigation bar, you can choose to view the calendar in Week, Month, or Agenda view . The view you choose dictates the style of the calendar window . By default, the calendar appears in Month view.
The sidebar  shows a quick-view calendar, your list of courses and groups, and undated items for your courses and groups.
Each personal, course, and group calendar is identified by a separate color that populates the calendar view. Associated assignments for each course or group will appear within the calendar view for each calendar .
By default, the first 10 course and group calendars will be selected and appear in the calendar view. To hide a calendar, click the box next to the name of the calendar . Calendars that are not active within the calendar view display as faded text 
This guide also has some great information on How do I use the Calendar as an instructor.
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