Want to get into more general Linux programming? The GTK library allows you to make games using the GTKGLArea, but also has a wide range of layouts, windows and widgets to make programs with user interfaces.
Getting Started
Link: gtk-getting-started
Want to get your toes wet in GTK? Start with the getting started
guide. It starts with a few basic buttons and callbacks and builds a
simple text editor by the end of the demo.
Platform Demos
Link: gnome-devel-demos
Where to go after "Getting Started"? The platform demo's page has a
few very simple applications which covers things like how to make a
simple image viewer or how to create and select a choice from a group
of radio buttons.
API Documentation
Link: Documentation
Likely your new home. All of the functions, properties, and signals
for all of the widgets
are well defined in the documentation. You should be able to find what
you need in there,
and if you run into problems you can ask for help on the Gnome #newcomers
IRC.