Ok to make a gun you would have to use a modeling program like milkshape, ac3d, 3ds max, blender etc. Then you need to rig your gun to an existing animation (not really for beginners).
To retexture your gun, first download Paint.net, then go into gamecore/guns/the gun you want to retexture/ then find the file named Gun_D.dds, Right click on it and open it with pain.net, save it as a jpg and it's ready for editing, then download gimp to retexture it.
Poloflece

Poloflece, not to be mistaken for polofleece, polar fleece or polar flece.