If you have AC 9 you can find a .pdf called
"Intro to object making in Archicad" inside
the documentation folder. This will give you
a good start making objects first by converting
3D models into GDL objects then making
objects using the GDL scripting language.
If you want to go deeper into GDL go to this URL
http://www.nottingham.ac.uk/sbe/cookbook/
and at the bottom of the page you can download
the .pdf version of the GDL Cookbook 3 the definative
book on GDL programing.
Peter Devlin