Users and/or the clients they are using will select which relays to publish and push their content out.

Depending on which relays you are subscribed to, you will be able to see different content.

But most common clients, whether on mobile (such as Amethyst & Plebstr) or on desktop (such as Primal, Iris, etc.) will automatically connect to the most popular relays, so you shouldn't have trouble seeing most content from your average user.

If you wanted to later to get into something more niche or to connect to some kind of group or subculture's internal messages, you'd have to look for those particular relays. Yet, I don't think that's much of a thing just yet.

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Hope that helps! Welcome to #Nostr, and have a great day ahead.

#grownostr