How to create a new cloth?

Hi, I saw people are able to create a new cloths to characters(not the CaC) and i was wondering how they were doing it(not just retexture the colors of different char costume and scale it to new char)

I saw a mod where the modder gave Teen Gohan ripped top, at first i thought he took Piccolo's ripped cloth but the ripped part was inverted at Teen Gohan mod, also some have made Baby's Armor, I was wandering which programs these modders uses and could love for a basic tutorial to understand the method

I tried to make myself as clearer as I can

Thanks in advance :]]