Textures Making

Hi i want to make a texture for this addon here
Please let me know how to create a texture and what programs i should use

You can use whatever program you like and VTFEdit for export/import. Please note that programs like GIMP ( And maybe photoshop ) offer much more functions, like editing alpha channel, etc, while programs like Paint and Paint.NET do not.

You could also use a PNG and use the new material override function to set it in-game.

How would i make or start the new texture for it

Extract previous textures by extracting the GMA with GMAD Extractor or SharpGMAD or w/e you prefer.