Okay you want to know the actual phyical results produced by the modification of these attributes.

Well diffuse is your color if you assign a texture to it, it will show the specific color at the specific UV that it is located at so diffuse is your color map.

Reflectivity(color specific) Okay if you assign a specific color to your reflectivity you will only reflect that color.

Specular. Specular is the highlight where a surface normal is directly facing you.

As for materials I know that 3d total has a good car paint tutorial as well digital tutors will have some tutorials on Mental ray and other materials. And I am guessing Simply Maya will also have some otherwise go to alias website download some of the free materials that you want you object to look like and have a look at what their attribute settings are.