A newsgroup is a communications medium that behaves in a similar fashion to email mailing lists, operating via a protocol known as NNTP. As newsgroups are a popular support and communication resource for many programming languages' communities, programmers will likely eventually need familiarity with them. As such, this page is intended to offer a quick introduction relating to concepts you are likely already familiar with so that you can use the resource effectively—and reduce social conflict when you get there.
Differences from email
On the server end, differently, they tend to operate differently from email:
Messages are stored on servers (often multiple servers) even after a user has read them; this allows multiple users to read the messages multiple times.
Since server capacity isn't infinite, messages are removed from the server on conditions set by the server administrator, and are usually checked and operated on automatically.
Messages are tracked by a unique ID, so a message sent to multiple newsgroups is known as the same message across all; this allows a reader of multiple newsgroups to instantly recognize that he's already read a message he sees in newsgroup Y if he read it in newsgroup X.
How to access
Most modern email clients also support NNTP, though there are also clients dedicated to NNTP. Try List of Usenet newsreaders on Wikipedia, to find one you may already be familiar with. Otherwise, you may try a web based gateway, such as Google Groups. (Google Groups is not entirely specific to newsgroups, but their service does allow access to it.)
If you use your own NNTP client, you will need a feed server. DMOZ has a list of such.