This article is for cPanel Accounts. Determine where your account is with this guide.
To use PHP, make a file and give it a ".php" file extension such as myfile.php. Inside this file you can put any HTML that would normally go in a Web page.
Anywhere in that file, within the HTML, you can put your PHP code (with the proper start and end PHP tags). You can learn more about PHP at http://php.net and http://zend.org You can find PHP scripts at http://hotscripts.com
WestHost would also recommend looking for http://w3schools.com/ for guides and help in learning to program in PHP and HTML.