Comment by fiatjaf

It's quite simple:

- You publish to, say, 3 relays.

- I follow you or want to browse your content for any reason.

- I connect to your 3 relays and fetch your content.

If I want to follow someone else and they publish to other relays I fetch their posts from those relays.

If some of your relays start censoring you you can move to other relays, or run your own, and I'll start fetching your content from those.

There's an interactive animation demo at https://how-nostr-works.pages.dev/#/outbox that explains it.