The Content Area Menu allows you to navigate and organize your course. This allows for streamlined, easy, consistent navigation across all courses. One of the biggest adjustments is that you cannot customize what is in your Course Navigation Menu; everyone has the same options. And while this will require you to think about your course differently, it is actually a great, time-saving tool for you. Your students have a consistent place across all of their courses to access course material. It does not matter whose course they go into, they know that they will go to modules to access course materials. Where Blackboard wanted to make the left column complicated, Canvas wants you to simplify it. The only complex thing in your course should be the learning and not the navigation of the course itself.
Instructure Instructor Guide: Course Navigation (Instructure Community)
Instructure Instructor Guide: Settings (Instructure Community)