Smr Simple!

Can someone please explain how to skin a model that a dummy could understand? I understand how you can take a pre-made template into a paint package and change it. I want to know how those templates are made from scratch. I see that the pre-made templates are made up of 4 files, a diff.dds, a emsk.dds, a nrml.dds and a spec.dds. Lets say you model up a train or building or whatever and it needs those files to skin it. Lets assume you are using 3ds max to model something. Are those 4 templates generated by the modeling program? I would hope you don't have to generate templates from scratch with paint shop or something. That would be insanely hard to do. How would you know where to place all the picture componets like windows, doors, wheels, etc onto the template? I have searched and researched on and off this board and I just don't get it. Please help a dummy.