A course's Enrollment Link (or Enrollment URL) is a unique URL that your instructor will provide to you so that you can enroll in your class. Each class section has its own Link that will not be used for any other course.
Enrollment Links follow this format:
(This is an example. Do not use this URL.)
The final section of the URL features four sets of four characters each divided by dashes. These sixteen characters are unique to your individual course. Once you click that link, type it in manually, or copy and paste it into your navigation bar, SI Cloud will allow you to enroll in the course.