The first step is getting a platform to develop the website. Yahoo Shopping allows you to quickly set up a site that is ecommerced enabled. There are other sites like shopitron and shopifi that are ecommerce platforms as well.
The first thing is to research and find out what your options are. This can be done online by going to BuildYourSite. com, GoDaddy. com, TipTopWebsite. com and Web. com/Websites. Find the one that is best suited for your needs.