DarkGDK is just big set of functions, you declare them in C++, which is entirely different and a bit harder than dbPro, but much more powerful and flexible. To make your own function you must:
1.) Declare what datatype your functions will return
2.) Name the function
3.) Declare inputs (optional)
Functions can be named anything you wish, for example:
void MyFunction()
{
INSERT YOUR CODE HERE
}
"void" is a keyword that tells your C++ compiler that the function will not return any data.
Just put what you want the function to do in the braces. I reccomend you follow through the tutorial series on this site:
http://www.cplusplus.com/doc/tutorial/functions/
That one covers functions, but it can teach you the whole language. If you stick with C++, even through the "tough times" it can have, you will know a very powerful and robust multi-purpose programming language.