That's not something to do yourself, I think. There are many, many companies that can make a webshop for you using, for example, Magento or Shopify.

Selling clothes has some specific properties, like being able to handle sizes and colors in a user-friendly way, the importance of pictures and a rather high return percentage. So be sure to have clear requirements, and I would advice to only select a company that succesfully made another fashion shop.