protected php page by passcode

Instructors can create a course, and this course is protected by a passcode; without this code, the students cannot enroll in this course. I have a table in my database called course, and it has a column called password the student can access the course page by course_id.

What I tried to do here when the student clicks on the course that is protected by a passcode, students should be able to enter the code for that course and then students who are enrolled should be stored in course_enrollement table so, he or she can access the page at any time, and without the need for a passcode.