Students and faculty are automatically enrolled by the Registrar's Office each term. If a student cannot see your course, it may be hidden from student-view. However, if you need to enroll a user (for a template or Org course), you can manually enroll users outside of the automated process:
For more information about how to enroll a user, you can read Moodle's Support documentation https://docs.moodle.org/35/en/Manual_enrolment