npub1jzk2v89wh9p8ta56nwaj4wt40wh6ut0e3xrakr0h5zzqe5qfzvnq3nq695 (npub1jzkβ¦q695) There's many different relays. You can connect your client to one or every relay.
Your account is a cryptographic hash so you're uniquely identified.
I think it uses blockchain or something, it's ridiculously bandwidth intensive.