This document provides an introduction to HTML and CSS. It defines HTML as a markup language used to structure web pages with tags, and CSS as a style sheet language used to describe how HTML elements are displayed. It lists common HTML elements like headings, paragraphs, and divs that can be block or inline, and describes how CSS can be applied internally, inline, or via external stylesheets to control things like colors, fonts, and layout. Key differences between HTML and CSS are also outlined, with HTML for structure and CSS for presentation.