Headings create a hierarchical representation of your document. Screen reader software can isolate a list of headings on the page that the user can scroll through, scanning until they find the header that is most likely to have the information they’re looking for.
When adding images to the MPS website, any text you enter as a "Title" will automatically become a heading.
Structure your document using paragraph styles (for documents) or heading tags (for web pages). Headings make the structure of your documents accessible to screen readers while improving both scan ability and maintainability.
You can apply document structure best practices in any written medium: from emails to research papers to blog posts. Everywhere you write, document structure can help you organize your work.
What does 'document structure' mean?
Document structure is the organization of a document into sections using headings and sub-headings.
Structure is critical for adaptive technology users, who rely on properly formatted headings to understand and navigate documents and web pages. Without this structure, there is no easy way to navigate a document because the document is read as a single long section. (BONUS: If you style your headings correctly and decide to change a font, weight, or size later, you can make one change and all of your headings will change, saving you oodles of time.)
How headings help
Learn to organize your paragraphs under descriptive headings, and apply "styles" to these headings in Word or Docs. This habit will make it easier for anyone to scan through your document and find the parts of the document they want to read, an attribute known as “scannability”. (Bonus: Once you apply a style to a heading, changing the style to a different font, weight, or size will change all of those headings in your document, saving you oodles of time.)
Source: University of Minnesota - http://accessibility.umn.edu/core-skills/headings