Help!

I know that some of you out there who read my (and my mother's) blog are a bit more technologically savvy than I am when it comes to page appearance. I am savvy enough to have gotten my Etsy account up and running, and I'll be "going public" selling my jewelry online soon. There is a way for me to take some JavaScript they provide & insert it into my page so that blog followers can see tidbits of what I am selling. Problem is, I can't quite figure out how to fit that into my design. I have figured it out to the point of customization, and viewing the Html, but I don't know where to insert it. I'm lost.

So, I need your help! Can you either direct me to a tutorial or give me your own advice? I appreciate it! My mom will also thank you because she is wanting to learn how to add things to her blog as well. ;)