This document discusses elements of HTML including headings, images, links, and cascading style sheets (CSS). Headings are used to determine different levels of importance on a webpage and can range from h1 to h6. Images are added using the image element which links to the file path of the image. Links are used to connect different pages together or link an external CSS. CSS can define styles and be embedded directly or linked via an external file with the .css extension. Embedded styles will override those in an external CSS file.