If you run shader_builder without any flags or input it should give you a basic manual page like this.
Basically, -m specifies that you want to make a matchbox instead of a lightbox, -x reads through the .glsl file and does its best to create an interface based on the input variables in the .glsl file and then writes that interface to an .xml file, -p will take the .glsl file and the .xml file and combine them to create a .mx file.
For even more information, you can run shader_builder with a --help flag for a more detailed manual page.