Paypal Sandbox?

Hi,
I got the basics down for setting up a Paypal Sandbox account. I need to test the IPN stuff. To test it it appears I need to know my IPN site url. How do I figure that out? I am going to try to do testing on two different carts, eShop and eCommerce to see which I can resolve the issue with first.

The other option is can I just use the site normally with the sandbox settings in place?

Thanks!