on the confirm page, there is a hidden element that allows you to set the return URL to return to your site.
the problem with paypal standard, though, is that it is not a real time payment method.
Once the user enters the paypal account and selects to proceed with the order, the transaction is placed in a queue to be processed on a first come first served basis and the user is redirected to your return page.
It is not posible at that time to know the success or failure status of the transaction.
paypal standard uses an IPN system to make notification of the order status when it is complete: