I have SeaMonkey installed alongside Firefox on my laptop simply because it's kind of fun to browse the web in a browser that sort of looks like the late Netscape Navigator, or early Mozilla browser. It's fun loading a Netscape site in it.
Does gnus still work? Is there a way to connect (preferable with the ability to post) with it for free?
How does one make a newsgroup?
Yep, you can get a free account at https://www.eternal-september.org/ if your ISP doesn't carry newsgroups (note it's for text groups only). Personally, I use Thunderbird as a newsreader (and my ISP still carries most newsgroups), there are also dedicated apps like Pan: http://pan.rebelbase.com/