There's a really good community feature on here called groups. It works like this:
1. Follow a group's account
2. You will start seeing posts on that topic
3. You can post to the group by @-ing it
It's more powerful than hashtag following, as all group posts are actively pushed to all of the group's members. No one misses anything.
Find out more about groups at https://fedi.tips/how-to-use-groups-on-the-fediverse/
If you're interested, try following one of the friendly active groups curated at https://fedi.directory/tag/fediverse-groups/
@feditips Can we search for groups on Mastodon directly?
From Mastodon's point of view, the groups look like ordinary accounts. You may see them appearing in search results alongside other accounts.
I just tried searching for "tea" on mstdn.social and one of the results was the tea group on guppe.
Groups have a "group" label on their profile if you're viewing them through Mastodon's web interface.