Okay, apologies for the many unanswered questions that are slipping past, am trying to answer as many as possible.

My timeline has just frozen completely.

Please check sites like https://fedi.tips and https://github.com/joyeusenoelle/GuideToMastodon/, they will answer lots and lots of common questions about Mastodon and the Fediverse!

If you are a techy person who wants to see technical details, you can find the official Mastodon documentation at https://docs.joinmastodon.org