Js Code For "confirm Email Address" Field

Right, "confirm." Not "verify."
Please help if you are willing.
It needs to also have a pop up or something that says it doesn't match what was previously typed. It also needs to require the character "@".

Here is what someone gave me in php but I can't get it to work:

PHP Code:
$first_email = $_POST['first_email'];
$second_email = $_POST['second_email'];

if($first_email != $second_email)
{
$error = true;
$message = 'Your email addresses do not match'
}

you can do whatever you want instead of $error = true; If you decide to go this method do something like this for your form

PHP Code:
<?php
if($error) echo $message;
else
{
?>
<form name="
.....
</form>
<?php
}
?>