How would I start my own Photography business?

Alright, i'm 15 years old at the moment. I know its possible to start your own business at this age, so don't tell me it's not. I live in Illinois and I'm needing to know how I would go about starting my own business. I know that I need to trademark my name and such, but who do I go to and whats some of the stuff I need to look at before getting started. I've won a thousand dollars for my photography and will be working in a studio this summer. Lay all the info you can on me! I'd really appreciate it.