There are several links that will help you...here are a few:

Numbered Headings
Understanding styles | ShaunaKelly.com
Understanding Styles in Microsoft Word
Microsoft Word Help, Tips and Tutorials – Making the most of Word in your business | ShaunaKelly.com

I know this is not what you ask for but, if you take the time to digest the information that you need (from "Numbered Headings"), the rest of the information will only help you further down the road.

HTHs