How to use / configure the Course Requirements module?
The Course Requirements module does not have a lot (any?) docu. But comment nr 3 of issue # 2148985 helps to make it work, i.e.:


Add a node reference field to your Course content type (to references other courses).
Go to admin/config/course/requirements and select that node reference field you just added.
Add courses through the node reference field.


After completing these steps, this is how it should work:


The courses you add in the field should block that course from being enrolled into without completing the referenced courses.
After completing a course it should also tell you what courses required that course for completion.