This document provides an introduction to HTML and XHTML. It defines HTML as the language used to structure text-based information in a document, and XHTML as an updated version of HTML that incorporates XML syntax. It describes the basic content that can be included in web pages, such as text, images, lists, and forms. It also explains how to properly structure an XHTML document using tags, and provides examples of common text formatting tags and other elements like headings, paragraphs, hyperlinks, and lists.