It says that you apply them in your graphic program. I've never worked with "textures" in that way, but from the sounds of the description at the site open the skin texture in your graphic program, then open the "texture" too. Copy the texture over top of the skin texture and then save it as a DIFFERNT name. Then you have to use MAT Pose Edit, to make the required files so that you can use the newly created texture in Poser.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi