Resources:

• Understanding Styles in Microsoft Word
• Managing Word Styles by Suzanne Barnhill, MVP
• Tips for Understanding Styles in Word by Shauna Kelly

What you likely want is to modify your heading styles to set the style for following paragraph.

You can use the keyboard shortcut of Ctrl+Shift+N to switch to the normal style. Do this without text selected to change it for the entire paragraph.

I do not recommend using the normal style for your body text. My personal preference is to use the Body Text style because any changes made to the normal style will cascade or ripple through many other styles.

• Normal vs. Body Styles by Suzanne Barnhill, MVP
• How styles in Microsoft Word cascade by Shauna Kelly

I generally disable linked styles. Character Style v Paragraph Style v Linked Style
I believe most experienced Word users do the same.

A good place to review how Word works is Basic Concepts of Microsoft Word - from Shauna Kelly