There are server variables. Use them in combination with forms.
you can use the $post when you use the POST method and $get with the GET method.
eg.
form.html
<form method="post" action="form.php">
<input type="text" name="textbox">
</form>
form.php
<?php
echo "$_POST['textbox']";
?>
This would print out whatever was entered into the text box...