Tons! Go to the GTK+ and Qt websites, and they have quite a few documents on how to start writing programs.
For programming under Linux, it is much easier than you may think. Really, though, you should pick a language to learn, and focus on it. I recommend Python for a budding programmer - also, there are many Python libraries out there for everything, including GTK+ and Qt programming. For these, Google for the "PyGTK" and "PyQt" projects; they should have documentation on how to get started writing programs.