Users can be Superadmins, Admins or simple users as far as the overall system is concerned. You only have those 3 choices, when creating a user.
When you have a course, and you enrol users to it, you can choose students, course administrators and teachers. So it's when you enrol users to a course that you declare who is going to be the teacher.
Hi,
it's like I said earlier: users only have 3 levels (Superamin, administrateur, utilisateur) in THE SYSTEM. Teachers, mentors, students etc are subscription levels only available when you subscribe users to courses.
So, first create a course (you will be automatically enrolled as a course administrator)
then go to the subscription button and subscribe users to the course: then you'll be able to set teacher, student and whatever role you may want IN THE COURSE.