I see. Thanks for the explanation and the links! Unfortunately I pretty much do not know what Twitter is, either. So I looked at the instances (?) you suggested and pretty much saw a doom-scrolling wall of random postings, which I find exhausting.
So when adding an account, I would just add to that wall of postings? How would people interact on such a platform? I am coming from Usenet, which had the greatest user interface ever (IMHO): you just follow-up on a posting and replies will pop up in your stream of unread messages. How would this work on Mastodon?
On Mastodon (and similar socials like Twitter and Facebook to a certain extent) you mostly follow people instead of themed groups like Usenet.
You set up your "wall of postings" (the "feed" or "timeline" in the jargon of socials) by following (subscribing to) the people you're interested in. On Mastodon you can also follow topics by following "hashtags", which are the sets of posts by any user tagged with a string preceeded by a hash character. For example, following the hashtag #retrocomputing will bring in your timeline the posts about that topic.
So, on socials, you typically scan your feed and the feeds of any additional hashtags you're interested in. For each post you can reshare it, reply (comment), or like it.
So when adding an account, I would just add to that wall of postings? How would people interact on such a platform? I am coming from Usenet, which had the greatest user interface ever (IMHO): you just follow-up on a posting and replies will pop up in your stream of unread messages. How would this work on Mastodon?