Do I need my IPN and an auto return url for prosites

I need to clarify something.

I have set up my ipn address in paypal.

Under profile > my selling preferences > website preferences

I have auto return on and it is asking for a return url. Do I just put my domain name or should I put something more specific in there or nothing at all?

I have payment data transfer on too.

It will be so great to have this working and not have to collect manual payments. I gave up last time but am determined to get it working correctly!