Think of Mastodon as an open-source Twitter with multiple servers ("instances" in Mastodon-ese) instead of the only twitter.com The servers interoperate through a common protocol, thus allowing any user on any server to follow and engage with any other user on any other server. The protocol actually makes it possible to interoperate with platforms other than Mastodon that are part of a larger system called the Fediverse, but you can ignore it for now.
The only software you need to get started is a web browser to use a web client, which is typically the Mastodon server you create an account on. Picking a server is the only potentially confusing choice, so for retrocomputing enthusiasts I recommend creating an account at https://bitbang.social or https://oldbytes.space Once you have an account on a server you can migrate to another one if needed.
For more on Mastodon see https://joinmastodon.org For any other questions feel free to ask here or follow me on Mastodon at @amoroso@fosstodon.org and ask there.
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.
The only software you need to get started is a web browser to use a web client, which is typically the Mastodon server you create an account on. Picking a server is the only potentially confusing choice, so for retrocomputing enthusiasts I recommend creating an account at https://bitbang.social or https://oldbytes.space Once you have an account on a server you can migrate to another one if needed.
For more on Mastodon see https://joinmastodon.org For any other questions feel free to ask here or follow me on Mastodon at @amoroso@fosstodon.org and ask there.