It’s an old federated message board system. Message boards are called “newsgroups “. It predates the web so it’s usually accessed via a special client app. To use it you’d need:

• A Usenet client app, called a newsreader. See Wikipedia. Many are probably abandoned by now.
• An account with a Usenet provider. A search engine will point you to several options. There used to be some free ones. If there still are, it would be a good way to try it out. But note that the free ones often don’t carry all of the newsgroups — they omit the binary groups, which are known to carry pirated software and, let’s say, diverse video content.