• Headers are titles and subtitles in a document
• Six header elements available: h1, h2, h3, h4 ,h5, h6
• Headers should be used in hierarchical order
• h1 for the main header on the page with several h2 defining the major sections etc
• Headings above h4 are not often used because the browser default rendering is quite small fonts
• With appropriate styling, they can be used if needed in large documents
• Paragraphs: p element

Example:

<h1>1. My Book</h1>
<h2>1.1 The First Section</h2>
<h3>1.1.1 The First Sub-Section</h3>
<h4>1.1.1.1 The First Sub-sub-section</h4>
<h5>1.1.1.1.1 The First Sub-sub-sub-Section</h5>
<h6>1.1.1.1.1.1 The First Sub-sub-sub-sub-section</h6>
<p>This is my very first paragraph in this document.</p>