Start with the list of servers here: https://joinmastodon.org/servers
If you want to discuss a specific topic, pick a server that is dedicated to that topic. For example, Fosstodon is a good choice if you are interested in free and open source software: https://fosstodon.org. You might also want to sign up on a server that has a community that is in your region or speaks your language.
Make sure the server your choose has policies that you agree with. Fosstodon's policies are here: https://fosstodon.org/about/more. The server rules explain what the accounts on that server are not allowed to do. That page also lists the other servers that are filtered, limited, or suspended on the instance.
Mastodon has multiple timelines. First, you have customizable personalized timelines containing posts from the users or hashtags that you follow. Then, you have the local timeline for posts from your home server, and the federated timeline for posts from your home server and all servers that are connected to your home server, combined. Your choice of server has the greatest effect on the local timeline.
You're not limited to one Mastodon account, and most Mastodon clients support using multiple accounts at the same time. You may want to try signing up on several servers and keeping only the accounts that you like the most.
I was asking why people use a particular server, and why would they recommend it.
I have issues with two points you mention :
> If you want to discuss a specific topic...
I do not. I have many interests, and do not wish to have multiple separate accounts for each. It does not make sense. I engage with others about many unrelated and completely different topics, putting them in isolated silos is one if not the greatest of Mastodon's main problems, in my view.
> You might also want to sign up on a server that has a community that is in your region or speaks your language.
Again, I do not.
I speak several languages natively, and have roots in different countries, where I am at different times.
This attempt to put the user in a box from the start, a tight box, as defined as possible in all respects, is a real problem. I find it hostile, honestly.
Edit : Should I think of Mastodon as if it was IRC ? I never have, I don't think that's what it's supposed to be.
Edit 2 : Thank you for your answer though. I should have mentioned that I am not trying to figure out how to use Mastodon, but was looking for feedback from people using it.
When I suggested finding a server with a specific focus, my intention was to highlight what makes Mastodon unique from monolithic single-instance social networks like Twitter. I didn't mean to come across as restrictive or hostile. The reality is that many Mastodon users don't use Mastodon as their only (or even their primary) social network, and that's why I emphasize Mastodon's strengths when I answer questions from people who are interested about Mastodon. I couldn't tell from your HN submission that you were only looking for general purpose servers.
Also, remember that regardless of the server you choose, you can follow accounts from any other server. The only exception is when the target server is suspended by your home server or vice versa. Any Mastodon account can be used to communicate with other users on different servers about different interests even if the account is located on a server that has a specific focus.
I wouldn't directly compare Mastodon (ActivityPub) to IRC, since IRC networks are independent of one another, while Mastodon servers are federated.
