Go to the ‘Catalog’ section.
Select the course you want to learn and open the course details page.
On the right, check whether any prerequisite course count is specified.
If yes, then click on the link to take to the prerequisite section in that details page.
Check if the prerequisite course has been completed. If not, click on the ‘More’ option to view the details of the prerequisite course and enroll to complete the course.