An NNTP server is set up by its system manager to know about some (at least one) nearby servers. With these servers, there is an arrangement that they will pass news to each other. Sometimes this arrangement is limited to certain news groups. Articles can be passed in both directions, and the servers compare article message-id headers to see whether they have any new news for each other.
(There are other protocols for communicating between servers, over dial-up lines for example, when there is no Internet connectivity. That is why there are many people who have no access to Internet can read and post news.)
Sometimes there are conditions attached to the news feed, which forbid for example commercial use being made of the data, or it being passed on by any other way than NNTP.
NNTP is much more efficient than HTTP for the case of articles which are going to be very widely read, because an article is only transferred once onto each site. Then, someone reads it, the WWW client only has to retrieve it from the local server, and not from the server where it started. NNTP servers will only allow local clients to access them directly, as to allow everyone in the world to access the same NNTP server would destroy this efficiency, and could lead to disastrous loads on the net and on that server. This is why you can't use just anyone's NNTP server. We get a lot of queries asking whether people can use ours. Sorry, you can't.
It may be that on your site there is already an NNTP server. Smart sites just give it an alias "news". If anyone on your site is reading Internet news then you could find how they have configured their new reader.
If you don't have an NNTP server on site, then someone is going to have to install it and arrange for a news feed from somewhere close.
When you have found one, then configure your WWW client to use it.
This doesn't scale very well, and in fact it would be more appropriate for them to run an HTTP server (or run an NNTP server and a server such as cern_httpd running as an HTTP/NNTP gateway). However, for these specialist groups, a URL of the form
nntp://host.dom.ain/news.grouphas been defined and will be available in future releases of the W3C Reference Library version 3.0 or later.