Ok it all starts with T-shirts. There are companies that allow you to create and sell T-shirts and other kinds of clothes that cost you next to no money, I say next to no money because you may have to buy a domain name for your site. Plus you make money selling them. Start with that, and once you start making a little money, then start your own designs, or not. Once you start your own clothing you can sell them on Etsy, Amazon, E-bay or your own website. What else can you create? DUH! Cosplay!!!! Go to the conventions tabs aNd browse through all of the conventions where people by the hundreds of thousands dress up. CLOTHE THEM! Facebook and other social media is a great way to get customers. It's all about taking the first step. There are software companies that have software that helps you design your own clothing. Build up to it.
Fashion Design Software
T-Shirt printing companies (some for free)
Image creation software
So you want to have your own clothing company?
Attention: I do not warrant or represent any of the companies named or listed on this site.