I point you there:
http://www.php.net/manual/en/tutorial.forms.php
To answer your question breifly PHP uses:
$variable = $POST["variable"];
or
$variable = $GET["variable"];
If you are using 4.2.0 < (ie 4.1.0 and below) or if globals are on you can just call the variable in your program, without using $POST or $GET like (say after POST or GET you have a variable named foo)
<?
echo $foo;
?>
Hope this Helps!