There are six headings in HTML. The headings are defined with the <h1> to <h6> tags. <h1> defines the most important heading. <h6> defines the least important heading.
Below are the headings:
<h1>I am heading one </h1>
<h2>I am heading two</h2>
<h3>I amheading three</h3>>
<h4>I am heading four</h4>
<h5>I am heading five</h5>
<h6>I am heading six</h6>
Headings Are Important in HTML documents
Use HTML headings for headings only. Don't use headings to make text BIG or bold. Use CSS to style the headings; change its font size, colours, margin, padding and background colour.
Users browse your web pages by its headings, so it is important to use headings to show the document structure. H1 headings should be used as main headings, followed by h2 headings, then the less important h3 headings, and so on.
Also, search engines use your headings to index the structure and content of your web pages.
To make all the headings readable to screen reader, all heading elements should be constructed hierarchically, i.e. if there is an h2 element on the page it should be preceded by an h1 element somewhere on the same page, if there is an h3 element on the page it should be preceded by an h2 element and so on.
Note: Browsers automatically add some empty space (a margin) before and after each heading.