This video will show you some of the ways to use Styles in Microsoft Word.
First, format your text.
In this case, I want the formatted text to be associated with the Style Heading 1. Select the formatted text. In the Home tab, in the Styles group, right -click Heading 1. Click "Update Heading 1 to match selection."
Now, you may apply the Heading style throughout your document as needed. Select the text to format and click on the Heading 1 style in the Styles group. Alternatively, you may use the Format Painter to copy and paste formatting.