General explanation about tox's p2p

I know it probably one of the most asked questions. But I can't find a detailed, or even a simple explanation.

How the software identifies an user without revealing the IP if the core idea of tox is p2p, and a centralized identification makes tox not p2p at all? Also, some informations about that hash functioning (tox ID) and how it replaces the IP sharing would be great to be at FAQ.