To make your website an e-commerce site, you will need to add a shopping cart. ShopSite offers to do all the work for you.
Otherwise, you can install a shopping cart yourself. Simply login to cPanel and click Fantastico De Luxe. Here you can quickly install CubeCart, osCommerce, or Zen Cart.
Learn about other reseller tools you need.
Unfortunately, HostGator cannot design your e-commerce site nor make your shopping cart do what you want. We suggest using ShopSite.