General Help with PHP and Forms

Please feel welcome to delete this if it’s too general. But thanks in advance for any help.

A while back I posted here, concerned that my lack of PHP skills would prevent me from being able to a) set up and b) work with WordPress. A number of you assured me that no PHP was needed. You were right completely — and I was able to set up WordPress without a problem.

But PHP has come back to haunt me: I need to use it to make a feedback form for a usability test for the site in general. (the site uses WordPress as the home page and for categories and archives, and some non-php pages for special features and essays). I’ve managed to get a feedback form going at this URL:

http://www.youthtopia.com/zphp/reportawork.php

The form works OK — the information is delivered by email. But after the user presses the SUBMIT button, the user is supposed to see a message that says “Thank you.”

The code I used for that, is this:

<?php
if (isset($sent)) {
echo “Thank you. Your information has been sent to Youthtopia.”;
}
?>

It’s not working at all: after clicking the submit button, the user sees the same web page of the form — no thank you message.

Ideas? Suggestions? … Thanks again … RB