Look at the links I gave you.

If you need help with styles:

• Using Styles to Format Text
• Understanding Styles in Microsoft Word
• Tips for Understanding Styles in Word by Shauna Kelly

You are dealing with paragraph styles.

1. The numbering must be set up according to the instructions linked previously.
2. Then set up one body text style for each of your headings.
3. Then set the setting in each heading style so that the style for the next paragraph will be your custom body text style for that heading.