In older versions of OneNote, you were greeted on startup with a built-in OneNote Guide that walked you through the basics of using OneNote. With OneNote 2010, the Personal notebook is the only notebook that shows up by default.
Fortunately, it is pretty easy to restore the OneNote Guide for OneNote 2010. Courtesy of Daniel Escapa on the OneNote team:
You’ll end up with a guide that shows the new features of OneNote 2010 and how to use them.