Answer:
You can not just enroll in a minor. You must be first enrolled in a major and then you can add on a minor. The minor is usually just extra set of courses you are required to take in that area.
College Major - A major is the main field that you want to specialize in while you are still an undergraduate at a college. ( A lot of units in college will be devoted into your major because that's going to be your career choice in life, that's why you are studying it.)
College Minor - A minor is a secondary field that you want to specialize in while you are working on your major. Generally, your major is what your intended career is, but your minor is something you pursue because of your personal interests.
For example: If I want to major in Education to teach primary schools (Which is elementary schools) then that would be my major for college. But, lets say that I love doing education, but I also love going to church to do ministries to help people out, then I can do ministries by making it a minor. Thus, my major is Education and my minor is Ministries. By doing this, you have more flexibility in what you want to do and it just gives you more options to work with because when you graduate college, it proves to others that you can do education and ministries because you put your time and efforts into it.