As we reported back in June, the feature allows you to send, request, and receive money inside the iMessage app or via Siri with the credit or debit cards you have setup with Apple Pay. All you have to do is authenticate the transaction with your fingerprint (or your face in the case of the iPhone X). The money you receive from the peer-to-peer payments will go to something called an Apple Pay Cash account, and from there, you'll be able to transfer it to your bank account, use it for purchases via Apple Pay in stores and online, or use it to pay someone else.
So far, Apple hasn't revealed when the update will arrive, but the additional wait for the new feature could be a relief for major players in the peer-to-peer payments space like Venmo, PayPal, and SquareCash. In the meantime, you'll just have to keep splitting your huge brunch bill with six other people the way you usually do.