My goal: Learn how to really use my camera before my WDW trip in December.

[Quicklabs]

We will be at BWV for 8 days in December. I plan on using many of those days as simply "photo outings" where I can really focus on taking great pics. (It'll be the holidays, so I'm so excited abou the possibilities) I love photography, but I just haven't really applied myself since getting a DSLR.
I have an Olympus E-500 that I've basically been using as a P&S to take pictures of my dogs. I really want to do better than that!
My first question: What does the histogram tell me and how can I use that to guide my phototaking efforts?
Thanks in advance for your guidance and for the many wonderful things I am already learning here.

[Groucho]

I would first learn about ISO and aperture before worrying too much about the histogram. Not that the histogram isn't important, but I think there's only things you should get comfortable with first.

To answer the question though, the histogram is just a way to measure exposure. A photo with lots of dark areas will show more to the left, and a photo with lots of white areas will show to the right. Areas that are too bright or too dark will be right at the edges.

I'm not sure if your camera can display an RGB histogram, but that will show you the same info, only broken down by the separate color channels. If your camera can't, software on your PC can.