The document discusses various HTML elements including headers, paragraphs, divisions, and attributes. It defines what a header is as the part of an HTML document that contains information about the page that is usually not displayed. It also lists the major 4 rules of HTML as using only lowercase for tags, closing all opened elements, enclosing values in quotes, and nesting all tags properly. Finally, it identifies the collection of networked computers as the Internet and the documents available for viewing on those computers as the World Wide Web.