In terms of time, this is no different than starting a business while employed full-time. Many founders choose to maintain their day jobs while working on their startup, so I believe you can do the same with school.
However, there are differences between the two:
You will learn a lot of valuable skills while in college. Those of us that went through college were able to take these important lessons with us as an employee and as a startup founder. If you drop out, you will miss out on some of these lessons/experiences. As @CaseySoftware points out in his comment, this includes building a support network.
You probably have very little in savings compared to those that work full-time for a few years before founding a startup. That brings us to your question:
how can/do people earn money while solely creating a business product?
You either have to work to earn money, or get someone else to support you. Unless of course you've worked for several years and have enough savings to support yourself.
In your case you could get a part-time job, or get your parents or the government to support you.