Can I use photoshop and gimp to make a skin

Can I use Photoshop and gimp to make a skin.

 

Yes.
A simple search could have told you that.

You'll need plugins for both of those to open and export dds files.
GIMP: https://code.google.com/archive/p/gimp-dds/downloads
Photoshop: https://developer.nvidia.com/nvidia-texture-tools-adobe-photoshop

 

and what file is the skin

 

vehiclename_skin_UVs.png is the template for the skin. Not all cars have this though.

(Replace vehiclename with the vehicle's name. e.g: hatch_skin_UVs.png for the Covet)

 

And what goes in the zip for a skin mod

 

Why not take a look at some existing skin mods? You can learn from them.

 

I will