If you leave the enrolment key area blank, then any site user can enrol in the course. Just make sure that Course Enrollable is set to yes.
You should also make sure that Guest access is set to Do not allow guests.
If you leave the enrolment key area blank, then any site user can enrol in the course. Just make sure that Course Enrollable is set to yes.
You should also make sure that Guest access is set to Do not allow guests.