There are a couple of options that I would suggest.
1) get a tutorial-type book on programming in C. Some will come with a CD or DVD with examples and other resources you need.
2) Find example programs that do things similar to what you want to do and use those as a model.
3) Search on iTunesU or similar resources to find videos of these courses being taught. Many prominent Universities now offer access to their courses free to the public.
4) If you are near a college or University, contact them to see if they offer any classes on this subject. Your best option may be at a community college. Some high schools partner with these colleges so you can actually take a college level course as a high school student and receive credit. Your high school guidance counselor should be able to help you find out more information about your options.
5) Check with your local library. Many libraries offer computer classes and they may already have something scheduled. If not, contact the coordinator of their programs and ask if there is other interest. They typically develop classes for which there is significant interest.