There are lots of interesting group accounts you can follow on here, they work like this:

1. Follow a group's account to see discussion of its topic
2. @ the account if you want to post to the group
3. The account boosts anything @-ed to it, be careful when you @ them so that you don't spam the group (spammers tend to be reported and blocked)

More info, incl. how to create groups, at:

➡️ https://fedi.tips/how-to-use-groups-on-the-fediverse/

I've listed some active and friendly groups at:

➡️ https://fedi.directory/tag/fediverse-groups/

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How to use discussion groups on Mastodon and the Fediverse | Fedi.Tips – An Unofficial Guide to Mastodon and the Fediverse

An unofficial guide to using Mastodon and the Fediverse

Groups federate much more effectively than hashtags, so they are a useful alternative to hashtag following. Group posts reach all the group's followers no matter which server they are on. This makes them very useful on very new servers that haven't built up many connections yet.

I haven't listed any example groups by @-ing as I don't want to spam any group's members. However, if you want to post to a group all you need to do is @ it.

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@feditips Try this in plain, human-centered English please. This clarifies nothing.
@smokler Groups are like mailing lists. You can join the mailing list by following the group (e.g., I can follow @/fantasy@/a.gup.pe - I added the slash so it doesn't spam the tag) for discussions about fantasy books/movies. Everything you post that tags this group will appear in the home timeline of everyone who follows this group. Of course, this means you will see all posts that tagged this group too. This works even if the poster is on a server that is not federated/connected to your server. You can explore what groups are available in the second link provided. I hope that helps @feditips
@geraineon Sure does. Thank you. I won't ask you to explain federated servers in plain English because, I believe like water flowing uphill, its not actually scientifically possible.
@smokler @geraineon Being "federated" just means that responsibility is spread out as opposed to being centralized. A good analogy is the post office system; every town has their own post office, and if you send mail to somebody local, it only goes through your local post office. If you send mail to somebody in another town, your local post office takes it to the remote post office, which then delivers it to the final recipient. Everybody in the system is part of a federation.

To extend the analogy, if one post office started delivering unsolicited hazardous materials to people, all of the other post offices may agree to no longer accept mail to/from them, which means they've been defederated. Mastodon works the same way; a server could become not federated either by choice or because other servers have agreed to refuse to communicate with them.

Let me know if anything there isn't plain English.