there are many threads throughout this forum where i talk about paypal standard and IPN. For your use, i would recommend not using standard. I would recommends express checkout, or payments pro instead.
the workflow of PayPal standard is this:
the confirm page posts the information to the paypal servers.
On the paypal server the costumer enters their information for how the transaction should be processed.
The paypal server excepts or denies this information and directs the user to the success or failure page.
At this point the transaction is line to be processed. it can take 30 seconds or 5 days for the transaction to got through. Once the transaction is processed the IPN post is made by paypal servers to the page you specify.
The drawback of paypal payments standard is that it is not processed real time the IPN page is never seen by the customer.
Instead of using payPal Payments standard, i would recommend using Paypal Express checkout, this is a free paypal option that is processed real time and does not require using an IPN post.
This really makes it a problematic system to use for something like whjat you are setting up.
For more details on IPN, see the paypal documentation here: