you only add your npub and a noteID of a note you post (which you basically have signed with your nsec with or without knowing this)
nostrnest then detects the note by which it verifies you are the npub "logging in"
Discussion
(unless it changed in the past months nostr:npub18ams6ewn5aj2n3wt2qawzglx9mr4nzksxhvrdc4gzrecw7n5tvjqctp424 nostr:npub12262qa4uhw7u8gdwlgmntqtv7aye8vdcmvszkqwgs0zchel6mz7s6cgrkj?)