Some of your better formatted Kindle books have a nice Table of Contents you can go to and navigate from.
To see the Table of Contents in any book that has one, press the Menu button at any place in the book. Move the 5-way selector down until the words Go To are underlined (selected), press in on the middle button (or the 5 way toggle switch on the Kindle 2 or DX) to see the Go To options. If they are available, you will be able to go to the Cover, the Beginning of the book, the Table of Contents, or a Location number. Move the 5-way down and to the right or left until the words Table of Contents are selected. Press in on the center button to make it happen.