That's it. A couple of points are in order. It is disabled by default, so you'd want to enable it by adding the following to your .emacs;;;enable narrowing
(put 'narrow-to-region 'disabled nil)
If you're confused whether narrowing is in effect or not, the modeline should have the word Narrow in it as a visual indication. Lastly, the hidden text and lines are not gone even if you save with narrowing in effect, so you really don't need to panic that you've accidently overwritten the entire file or any other pant turding fear!