Think about relays like a server or as i like to say its the nostr highways.. you could be on highway 23(relay) while the party and cool notes are on highway 21(relay) so if you dont have highway 21 you missing out on notes..

Relays act like the bag of notes.

Twitter has one bag of notes tgat they control who sees what you see.. one centralized server

Nostr has a bunch of servers(relays)

This is the ghetto explanation 😂