First you need to choose a domain. Example: If you're selling shoes that light up, you may want to choose something like www.lightupshoes.com so people know exactly what you do and it would be easy to remember. Second you need to figure out how you want to build it. If you don't know how to build one, I suggest using wix.com, shopify.com or another website building site. Next you want to take your time researching your competitor sites. Do they have alot of products? How is their page laid out, etc. Take this into account when building your site. Use some of the good things that they do, but also try to be different as well. Maybe incorporate a blog talking about the latest shoes that came out for example. Once you have built your website you want to make sure you are updating your products and content as often as possible. You want to register your site with all the major search engines. Create listings in all the free directories and just promote the heck out of your site.