a .CHM file is a Compiled Help File.... typically, when you bring up a help file from an application(such as pressing F1 inside Softimage XSI or 3DMax) the file that is displayed is a .CHM file.. its a format of file that windows can work with kind of, to display text in a "help file format"(with heading, and subject, search, content, index etc)
The help file for DarkGDK contains a list of the function names, under their respective headings, each has a paragraph or 2 explaining the function and what its parameters are used for..
However, many of the commands contained in the GDK do pretty much what their name says, and their parameters are usually named as what they represent. One of the best ways to learn how to use them and what exact effect different paramaters can have when you call the functions, is to experiment with them.. Load up and change the values in the samples to see what kind of effect it has, add extra commands in to try and make the samples act differently..
Eventually you will end up with a fairly good knowledge of how all the commands work and how to achieve what you want... from there, you can do anything you can imagine
As to actually looking inside the libraries for the GDK, thats something we cant do, they arent text files as Lilith said above, the source code that these libraries are compiled from though, is something that we arent supplied in the free version(I dont know what kind of lisencing TGC do with GDK in relation to source code, you would need to contact them about that)
If it ain't broke.... DONT FIX IT !!!