A role is a collection of permissions defined for the whole system that you can assign to specific users in specific contexts. The combination of roles and context define a specific user's ability to do something on any page. The most common examples are the roles of student and teacher in the context of a course.

More on roles and permissions on the Moodle website (may be available in English only)

Enroll a user

Steps: Course administration > Users > Enrolled Users

  1. Select Enroll users.
  2. Select the role from the menu. The default role is student.
  3. Search for the user.
  4. Select Enroll.