Hey Mastodon server administrators!
A lot of new users are wanting to use the "what's happening" feature to see what kind of public posts are made on your server. You might want to switch it on?
You can switch it on by going to Preferences > Administration > Site Settings, and tick the box marked "Allow unauthenticated access to public timeline", then click "Save changes".
Also, I would strongly advise you to NOT tick the box marked "Include federated content on unauthenticated public timeline page". All this second box does is fill your "what's happening" page with posts from other people's servers, and it doesn't really help people know what your server is like.
Mastodon.social definitely does exist, it's at https://mastodon.social. It was the first Mastodon server, it's owned by the lead developer of Mastodon. It has sign-ups closed though as they're trying to encourage people onto smaller servers. It's bad for the network if there are too many people on one server.
https://mstdn.social is a totally different server with a different owner.
They're just two different servers that happen to have similar names.
A general-purpose Mastodon server with a 1000 character limit.