To check if you have view-only or editing privileges within a class, visit your settings by clicking your avatar at the top-right. Scroll down and you will be able to see which classes you can edit and which classes you have "view-only" access to.
"View-only" simply means your collaborators may only view your class, without the ability to edit, add, or remove any items in the class (e.g. assignments).
Collaborators with “edit” permissions can add and make changes to your class. This collaboration type is ideal for co-teachers, special education teachers, or departments where subjects and students overlap. Collaborators with “edit” permissions can create, grade, and leave comments on assignments. They’ll have access to class and individual student reports.
To learn more, watch this video.