As a student, why can't I edit in the OneNote Class Notebook?

When you open your notebook, you should know that there are three distinct sections of your OneNote Class Notebook:

Collaboration Space: This is designed for everyone in your course. Collaborate with your instructor and classmates in a space that everyone can contribute to. Think of this as a giant shared doc. 

Content Library: Only your instructor edits this space. Think of this as a file cabinet in the classroom with all of the classroom's previous handouts and resources. Students cannot edit anything in this section, and will get a "Read-Only" error.

Private Notebook: This designed for your personal space, and for your instructor to review your notes. While you and/or instructor have access to this space, other students cannot see your assignments.

Your instructor will often make assignments and prompts in the Content Library. Note this is a space that, as a student, where you do not have edit access. 

Your instructor will most likely distribute a prompt or assignment to you. While the original copy may appear in the Content Library, you will not be able to edit the original copy. Make sure you are in the Private section of your notebook by first clicking on your name, then opening up the sections in your private notebook.