You subscribe to the groups you want to read and then can download the messages and start communing. Most sites hosting newsgroups claim to own the posted material. There have been cases of people not getting hired after a search of the newsgroups revealed extreme opinions. Like any social interaction, you can pick up viruses if you open attachments to newsgroup postings. Don't do it.
Email lists rebroadcast email received by the listserver to everyone who has joined the list.
You generally should introduce yourself to the list and you need nothing but your email program to participate. They often offer a digest version so you don't get zillions of emails a day, but a consolidated version. To get the most out of the experience acquaint yourself with the rules and freely confess to being a newbie. New folks are welcome but attitude is not. This site wins hands down as a source of invaluable information on Canada's past.