It's kind of like making an email account. First you pick where you want your email to be (gmail, outlook, proton, etc...), then make your account.

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If you're brand new, pick where you want your account to live.

- General worldwide website: mastodon.social

- or pick a website by topic: https://fedi.directory

- or pick a website by locality: https://fediverse.observer

Your starting global feed will have different users/posts based on which website you pick.

Check out which one you want then make an account there.

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Now choose some people to follow:

- Either in the global feed on your website

- or choose people by topic: https://fedi.directory

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Then people who you follow will share posts from other people, and you can choose if you want to follow them too.