Under Course Enrollment tab, Choose the details like course name, group / section and name of the teacher from the drop down menu and click on add button.
This will add the group chosen to that particular course.
To enroll individual student / Teacher
Under Course Enrollment Individual tab, Enter the email, select the type of user (i.e.) Student / Teacher, select the course and section from the drop down menu and click on add button.
This will add the Student / Teacher chosen to that particular course.