Network news is arranged in the form of newsgroups geared to different topics for discussion. USENET is a set of newsgroups of global interest and the term has now become and umbrella term including many local newsgroups included on a server. USENET does not require the Internet since it predates it. There are many different news reading programs for USENET (including rn, trn, nn and tin on Unix, e-mail front-end newsgroup readers. Windows based readers Win VN, xrn etc.) You can also access it via the WWW but this only enables you to browse, not to reply or post articles, "subscribe" or "unsubscribe" to lists. Depending on your institutions servers you may find it easier to use a specially set up newsreader enabling you to make your own input to a group instead of the "read only" situation on the WWW.
Newsgroups of interest to physicists include news:sci.physics and news:alt.sci.physics.new-theories
Further newsgroups can be found through the Newsgroup search program from Deja News.