This is a relatively common occurrence....Where one invests time and effort in to an html site and then just wants the "add to cart" function.

If you are stuck on this there are other avenues for you but Zen Cart is not modular and can not be sliced up to fit what is described above.

You need to evaluate the the future of this site and as you know a bit of html you also know that each product page must be built individually in your html scheme. And then if and when you change a design item, you have to edit all pages.

If you follow the leads and advice in using Zen Cart, you will make Zen Cart look like your site (header, footer, colors etc) Then Zen Cart will build all pages from the elements dynamically. Creating a product or a group of products then becomes a simple matter of entering the product info and image and Zen Cart creates the page.

Your site is one that can easily be transferred into Zen Cart. And there is much assistance here on the forum but you should first read the FAQ's and the wiki for the basics.