<h1> - <h6>
Headings define the structure of the web page. It is important that you use them correctly. The tags are from h1 to h6: <h1>Title</h1> - <h6>subtitle</h6>. For the most part users only scan down the page so headings are important to get their attention.
The importance denoted by each number is in descending order with <h1> being the most important. Except for <h1> each heading is a subset of the immediate higher number. By default each heading has a size. <h1> being the largest and <h6> the smallest. You can change the sizes with the CSS but should still keep the visual progression with <h1> being the largest etc, then users can see the importance of information on the page.
Section 508Section 508 states the requirements for those developing, maintaining or us of electroic and information technology Headings are extreamly important for 508 they are used by screen readers to read the web page. Screen readers are used by users with visual disabilities.
Section 508 requires that when Federal agencies develop, procure, maintain, or use electronic and information technology, Federal employees with disabilities have access to and use of information and data that is comparable to the access and use by Federal employees who are not individuals with disabilities, unless an undue burden would be imposed on the agency. Section 508 also requires that individuals with disabilities, who are members of the public seeking information or services from a Federal agency, have access to and use of information and data that is comparable to that provided to the public who are not individuals with disabilities, unless an undue burden would be imposed on the agency.from: www.section508.gov