This document provides an introduction to embedding PHP code in HTML documents and sending form data from the client to the server. It discusses using PHP to echo HTML tags and strings. It explains how form data is sent via GET and POST methods and how it can be accessed in the PHP file specified in the form's action using the $_GET, $_POST and $_REQUEST superglobal arrays. It also covers uploading files via HTML forms and accessing file data in the PHP file using the $_FILES array.