PayPal integration - instant payment notification (IPN) - paypal

Question

I am having doubts on how to implement PayPal IPN. I have created a button, and it has the variable notify_url defined:
<input type="hidden" name="notify_url" value="./ipn.php" />
In ipn.php file I have put this code (from Integrate paypal):
<?php
// read the post from paypal system and add 'cmd'
$req = 'cmd=_notify-validate';
foreach ($_POST as $key => $value) {
$value = urlencode(stripslashes($value));
$req .= "&$key=$value";
}
// post back to paypal system to validate
$header .= "POST /cgi-bin/webscr HTTP/1.0\r\n";
$header .= "content-type: application/x-www-form-urlencoded\r\n";
$header .= "content-length: " . strlen($req) . "\r\n\r\n";
$fp = fsockopen ('ssl://www.sandbox.paypal.com', 443, $errno, $errstr, 30);
// assign posted variables to local variables
$item_name = $_POST['item_name'];
$item_number = $_POST['item_number'];
$payment_status = $_POST['payment_status'];
$payment_amount = $_POST['mc_gross'];
$payment_currency = $_POST['mc_currency'];
$txn_id = $_POST['txn_id'];
$receiver_email = $_POST['receiver_email'];
$payer_email = $_POST['payer_email'];
if (!$fp) {
// HTTP ERROR
} else {
fputs ($fp, $header . $req);
while (!feof($fp)) {
$res = fgets ($fp, 1024);
if (strcmp ($res, "VERIFIED") == 0) {
// check the payment_status is "completed"
// check that txn_id has not been previously processed
// check that receiver_email is your primary paypal email
// check that payment_amount/payment_currency are correct
// process payment
}
else if (strcmp ($res, "INVALID") == 0) {
// log for manual investigation
}
}
fclose ($fp);
}
?>
The question is how do I receive the notifications in the user's account? What kind of code do I need additionally?