An important distinction to understand is the difference between a student signing up for and student enrolling in one of your courses. 

When a student first comes to, they need to create a user account in order to do anything.

After that point, the student will be able to log into account, but they won’t have access to any of your course content. They will need to enrol in a specific course in order to gain access to its content. If your course is free, students will be able to enrol with a single click. A paid course includes a checkout process to process their payment.