I was thinking, since I want an application layer for my operating system, how or what would be the best way to write, or better understand how to write, my own graphics device drivers or software to enable application layered software to request data through my graphics system (I.e. windows, icons, mouse pointers).

I don't need every little detail, I'd just like some possible insight on the procedure one may accomplish this feat in, perhaps the best way to understand the interaction between the graphics GUI rendering software to the hardware interaction directly, and the application software requesting the graphics driver itself.