This is a pretty lofty subject to tackle in a forum-length discussion. How familiar are you with Family creation? All the geometry that is created in a Family has a "Material" Parameter and those geometry "Material" Parameters must be associated to a Family Types Material Parameters to be able to access them and change them in the Project. Am I making sense? If so, I've just scratched the surface. Like I said, this is a lofty subject.
...you might be better off spending a couple of days researching the subject on the internet. FWIW.