I didn't realise you wanted to input new records from here.
I've modified the subform by changing the query links and adding two more fields to the query and using them as combo boxes to look up the student and course.
I've also added in a bit of VBA behind both of the combo boxes to refresh the data when a student or course is selected.
What you can't do 'properly' is add new students or courses from this form. I wouldn't recommend it because all of the student or course fields may not be displayed once the form is fully developed - so I've locked those fields off.
See attached