I've been learning about different texture maps I want to know how to make them.

I have yet to see a tutorial about how to make them, like one of the videos explaining materials and textures had created a map to make his final material look like it had a bunch of scratches that weren’t in the original texture, but again it didn’t say how, only that it was a black and white image. I don’t even know the proper name for this kind of texture map. I also want to know how to make, normal and specular maps because I feel it can only help. So is there a place I can go to learn these kind of things?