Your question is too generic. Web Commerce can be seen as a part of E-Business: E-Commerce. And it consists of different technologies (see image)
It depends on what purposes you have in mind. The E-Commerce is alone complicated. It combines Web-technology and beside the traditional browsers it could include, for example, mobile phone as an end accessing device (e.g. bankcard Reader, etc.) In this case you have to involve Smart Phone development into your development project.
For the start: click HERE.