Introduction
The mobile age is as well a challenge for commercial websites to provide e.g. an e-shop running compatible on different mobile devices. See also: Wikipedia: M-commerce !
Retailers are faced with a wide range of various hardware & software conditions. First of all, they have to decide between web or native applications. All these app types keep different advantages & disadvantages. A native shopping app is on the one hand more expansive to build up than a web shopping app. On the other hand a native app allows to use more features of a given device in comparison to a web app. A web app is platform indepentent but mostly doesn't ensure such a high user expierence like a native app.
Online retailers have to managage a huge amount of data (product catalogues, customers's information, supplier specificatons etc.) via their shop software. Additionally, they have to assure the security of all electronically safed data. This has to be valid for their mobile applications, too.
The task: Creating Web App
A web app is mostly created with HTML5, CSS3 & Java Script. And it's executed trough a mobile browser. See also Wikipedia: Web app & Jonathan Stark, O'Reilly: Building iPhone Apps with HTML, CSS, and JavaScript !