Well, if it was me, I'd use something like osCommerce. It's specifically designed for e-commerce websites. However, there are other routes you can take. Such as manually developing your website using something like Dreamweaver, and adding a shopping cart system into it. And then there is the basic PayPal route, where people click on the button and it takes them directly to a secure PayPal shop thing.
There is also eBay, but I presume that's not what you are interested in.
You will need your own domain name and hosting. I would not recommend you use those rubbish free websites. You wont get one sale if you use those.
Anyway, what do you want to sell?