Teachers frequently use a messaging tool linked to a specific assignment or quiz in Canvas to send important email reminders. The reminders go only to the students who haven't turned in an assignment/quiz/test, or may have a low score that can be made up. If you have an observer account, you will receive this message as well. If you do not have an observer account, only your student will get this type of message.
Observers can also see all the coursework posted on Canvas. This can help if you need an extra copy of a lost assignment, or you may be able to watch a video that the math teacher has posted. You can also ask your student to login and show you this information as well.