Problem:
In the real world there are e-commerce service providers who offer some degree of service products to your e-commerce web site. Some offer a turnkey (everything you need) service and some offer components such as carts. PayPal is an example of an e-commerce service provider. While they do not offer web sites and hosting (perhaps just around the corner) they do offer cart hosting. Every service provider offers a different take on providing their service and various interfaces. UPS is another example of a service provider.
Find an e-commerce service provider online and analyze their offerings along with a detailed view of how it may work and integrate with a functioning e-commerce web site. DO NOT analyze an e-commerce site selling products. Focus on providers of e-commerce turnkey products or sites having e-commerce tools.