How product detail can be sent to client in Paypal IPN

[sayfrndship]

hello,

i am good to joomla but new to virtuemart, i m doing first experience with it. what i need

that when IPN is sent , I have PIN code field in product, that i need to sent to customer after he has paid from paypal. I am reached and find that IPN notification file is notify.php . but not getting proper help that can tell me exact flow of virtuemart framework so i can find out, how i can get

user id while i m in paypal site and paying, and get current items in cart,
i need these two things, so i can get item in cart and their details to send to customer in email,

any one help me.