Hmmmm, this is very homeworky
Looking at the question you need a form, the form submit option onSubmit="" needs a function called isCourse
Suggest that the function isCourse is written so it returns a value of true or false so when using it in the form onSubmit="return isCourse(this);" will cause the form to submit if true or if not true the form submit is ceased.
passing the generic object this will allow you to address the specific field you need to test in the form submit as "this" will be all the forms inputs and options lists, etc.
Your HTML file should contain your validation script and the form that you are going to use / validate.