In HTML heading tags are all titles or subtitles in the whole webpage.

For this purpose, heading element from <h1> to <h6> are used. There are six levels of heading tags that HTML describes. Let us add more, heading elements are block-level elements, as we have been describing in the previous tutorials, block-level elements occupy 100% width of their parent and break the line before and after.

There are six heading elements from the highest level to the lowest level (h1, h2, h3, h4, h5, h6). The heading tags h1, h2, and h3 are the most important, others are the least.
Syntax

<h1>Gitdemy</h1>
<h2>Gitdemy</h2>
<h3>Gitdemy</h3>
<h4>Gitdemy</h4>
<h5>Gitdemy</h5>
<h6>Gitdemy</h6>

Why do we use the heading tags?​

For example, if you are writing an article on a web page, all content in the article is written in plain text. you will want to make the title in bold and large font size so that title and content look separate from each other.

Further reading - HTML headings tags