I get confused myself sometimes.
The "store window" is the actual flash component you see in your auctions that displays up to 20 pictures of other items you have running.
You'll notice that inside the store window is a link that says "Click to see my other items". Clicking that takes you to a webpage that shows all of your active listings, sorted by time remaining. This website is what I typically refer to as the "showcase". It's a showcase of all of your items and also contains a page for "about me" information.
Let me know if that helps.
-Kevin