For each assignment, there is a "Private Comments" Section. You can communicate with your teacher. Your comments will only be visible to the teacher.
Teachers are able to comment in the same "private comments" section
Teachers can add comments to the documents you upload. To check out these comments, you will have to open your attachments and then view the comments there
For teachers:
This quick video will show you how to add comments to an image submitted by a student. You can even set up a comment bank for frequent feedback! What a time saver!