Use a packaged catalog service. Packaged catalogs are a service provided by an e-commerce vendor, where the merchant builds a web site using a template and simple forms to enter their specific product information. The product listings, web pages and shopping cart all reside on the vendor's server. This method has the benefit of being very quick and simple. But it does not permit custom designed web sites.
Security is handled by the catalog vendor.
The merchant purchases hosting services as well as a shopping cart service from a vendor. The merchant is responsible for designing and building the web site, and uses special codes to integrate the shopping cart features into their web site. Security is handled by the hosting service. When a merchant has an existing web site, and wants to integrate a shopping cart into this site, an offsite shopping cart service can be purchased. This is very similar to the previous method, except that the site resides on one server, and the shopping cart resides on the offsite services server.