Can I ask what is probably a very simple question.

I am quite fluent with xhtml but the problem I have concerns the rest of building a website!!

Basically if I was building an online store what package would I need? I have being trying to research zen cart, is that used? And if it is, is this where you get the "view cart" icons etc.

Is there something that is used to build online stores, preferably open source?

Thank you and apoliges if i am in the wrong place.
C