Use of appropriate Headings is one of the most important aspects of good readability, useful text content structuring and search engine optimisation. Heading styles should always and only be used for the structuring of longer pieces of text content.

See example headed content.

This is what Heading 1 looks like

This is what Heading 2 looks like

This is what Heading 3 looks like

Anything below heading 3 should be bold text

Heading styles are accessed from the Format > Formats > Headings editor menu.

Only Heading 1 to Heading 3 should be used

Heading 1 is the Section name in most page layouts, which appears by default at the top of each main content area. This first level heading is already built in to the design of every page and acts as a page introduction.

You should be using Heading 2 for any on-page headings and Heading 3 for any sub-headings under Heading 2.

If you wish to further sub-divide your content below Heading 3 then use bold text to indicate this.

Don't skip headings

Headings should follow a logical order on the page. Starting with 1 and decreasing from there.

Don't use Heading styles to emphasise text

That's not their purpose. Using headings only to change the size of text for appearance purposes will detract from the accessibility, meaning and maintainability of the page, and have a detrimental effect on SEO.

Instead

Use bold for emphasising a sentence.

Or for emphasising a word or an entire phrase in a sentence.

Use Formats > Paragraph highlight - maybe with bold.

Use Formats > Button links if the text is a link with short text and a call to action:

call to action