Trinsec.org
Trinsec.org
Trinsec Dot Org
This is a privately run server by Trinsec.
If you want to join the Fediverse, I can recommend vivaldi.social (1337 character post limit instead of 500), mstdn.social or masto.ai.
Dutch people might feel more at home on mastodon.nl.
(Those above are all Mastodon servers as that's probably the easiest platform for a beginner to join.)
Make sure to read their rules before joining.
Just don't join the huge instances like mastodon.social, they're too big and laggy and spammy. For your own sanity, please choose a moderately-sized instance.