The document provides examples of basic HTML code and instructions to check how changes to the code affect the rendered webpage. It demonstrates how replacing <p> with <a> makes the text a hyperlink, and adding <strong> bolds the text. It also shows how <li> defines list items and <nav> creates navigation, and introduces the href attribute to <a> to define hyperlinks. The examples are intended to teach HTML syntax through experimenting with code changes and viewing the webpage output.