How do I add individual teacher/student/non-editing teacher/observer to a course?

If you are permitted to add students to your course this is how you proceed:

1. From the course administration block click more first and then users/enrolled users.
2. Click enroll users button.
3. Search by email address for the user you would like to enroll.
4. Make sure the correct role appears at the drop-down at the top.
5. Click enroll button and finish enrolling users.

The user will now be enrolled in the role you selected in your course.