Gloss is a black and white image. The whiter an area, the more reflective it will appear. To be honest, I've never understood the difference between specular and gloss textures.
Normals are bluish, and give the illusion of fine surface textures. Wrinkles and such.
Diffuse is the basic visible skin texture.
You can find examples in Custom\Atom\Person\Textures\FemaleBase