Newbie Help

[gkcbn]

Help! I have a shopsite website already up & running. A company put it up for me and they are no longer in business. Now, I'm left with a bit of a mess. Some of the pages, header/footer are not in shopsite. Specifically, the home page. I am new to html/coding and have very little knowledge. Where do I begin? I've read about the custom templates but don't know how to get them into my site and how can I test it without mucking up the rest of my site?
Thank you in advance--

[ShopSite Lauren]

What's the URL to your website?