Reading the books on the history of Unix and Linx won't hurt. But as mentioned, the commands (for reading news and groups you are looking at are ancient. They were popular and important when most people used a console terminal interface for everything. You would likely get better mileage by using a graphic (web) interface for your studies, news, and groups. Wikipedia has lots of information on the historic development and stages.
The tone of your message sounds like you might be interested in learning Unix. If that is the case, you can use a resource such as Tutorialpoint's Unix Tutorial, which will also provide some history of Unix along with an outline of the various commands and usage. Becoming familiar with some of these details may fill in some of the gaps you are having in trying to understand the ancient news readers that you are exploring.
There are many applications for reading newsgroup. Thunderbird has a newsgroup reader feature (http://www.fastusenet.org/thunderbird-tutorial.html).
Usenet probably appeared to be free to most people who were using it back in the day. However, they were using a service of their ISP who was linked as a Usenet feed (server). To be effective, the server host a huge amount of data. I haven't checked lately, but I'm sure it's not as common these days for most ISP's to invest in the resources.
There are a number of Usenet providers. Most of them charge a fee and provide readers and search engines for their clients. This is an example list: https://usenetreviewz.com/best-usenet-providers/
Google became a popular free Usenet provider. They eventually started calling the groups on their server, Google Groups. With time the regular Usenet groups on the google server became somewhat hidden, and you mainly just see the Google groups of the feeds. If you look close enough you can find the other Usenet groups. However, their reader interface has lost the ease of use of the regular Usenet groups (outside of their own groups).
In more direct reference to your question concerning reading the groups with rn, tin, trn, you would have to first locate the server you want to use and configure the text-based client for that server.
Your message is indicating that your server isn't configured. You can test it out with some of the newsfeeds in the list above. If you sign up for one of the fee base newsfeeds, they will provide you with a client for accessing. You'll then be able to compare the access information they provide you with for the information in your trn client files. This will get you past the connection refused and server unavailable error messages.
