Search engines use the headings to index the structure and content of your web pages.

<h1>This is heading 1</h1>
<p>This is some text.</p>
<hr>
<p>This is some other text.</p>
<hr>

Are defined with the <h1> to <h6> tags.

<h1> defines the most important heading. <h6> defines the least important heading.