you can use any graphics software to create a toribash texture, i personally use paint tool sai but you can use loads of different ones, gimp is probably the best for a beginner.
to use a toribash texture you much purchase the texture item of the area you want to texture, most people start with a 128x128 head texture worth 2000tc. you must buy texture items for all of the tori to texture him fully.
i would advise getting practice, looking at tutorials and getting to know the market for textures before you start making them. selling your textures is a good way to make money for buying the texture items.
im not the best at explaining things but i hope i helped a little!