I don't know - you haven't posted your page ;)
In this simple example, the PHP processing script would go into a file for processing, so let's call it "process.php".
Then you'd point to it via the form action attribute, so it is actioned once the form is posted;
I suggest you Google a few PHP form tutorials first though.
<form action="process.php" method="post">
It would be nice if you post the code you are working , then members can add your requirement in that code and it will understand and clear your doubts.
Thanks to everyone, I think I'm on my way now.
I am reading PHP, slowly!