Well, the first thing you should learn is how to do a search and see if the question you're asking has already been answered. Check the forums; there are some stickies and plenty of other threads by people asking how to get started. Also look at our wiki.
It's good you're starting young. It doesn't really matter which language you start with; Python and C# are commonly recommended here (and then learn C/C++ later on). Find some online tutorials and/or get a book from your library, and work through them. The most important thing is just to keep practicing and writing programs. You'll get good at it if you just spend some time doing it every day.