Lets start with the basics. PHP, like any language has rules to it, and you must follow them or PHP will not understand what you are trying to make it do.
The Basics
Here are the sources used in this tutorial:
simple.php
<?php define("HAPPY", 22); //echo HAPPY; $simple = (int)$_REQUEST['s']; $tires = $simple*HAPPY; $tires = 1.06*$tires; echo 'You need to pay us $'.$tires.' in cash today for your '.$simple.' tires.'; ?>