Headings are an important part of any document, visually and with a screen reader. Headings tell a reader the title of your document, and the sub sections within a document.
Each sub section is part of the larger section before it.
Screen readers interact with headings that are properly marked in a few ways.
One way is that screen readers allow a user to skip from heading to heading to quickly navigate through a document.
This is analogous to scanning through a document by just reading the headings.
Another is that the screen reader will announce what heading level a heading is. But screen readers cannot read text that looks like a heading without it being properly marked
as a heading.
Headings are labeled from 1 to 6. The first heading, and often the title, in any document is the Heading 1. There should only be one Heading 1 in your document.
Each heading contains information within it. When you have a heading inside your Heading 1, you label this as your Heading 2. Headings within your Heading 2 are labeled Heading 3.
Take this web page for example. On this website we have our heading 1 at the top telling us the name of the website.
Then we have our heading 2 telling us the name of this page. Then this section has a heading 3 which is a subsection of the heading 2.
Each heading contains information within it that is sectioned out by other headings.