When you subscribe to a mailing list you are actually subscribing to an email based meeting place. News groups are public message forums, just like bulletin boards. The forums are divided into groups and then subcategorized by topic. Froggernet currently provides access to over 73,000 newsgroups. First you need to obtain a news reading program.
Most current browsers ship with a news reader as well as an email client.
After downloading the list of available groups, you should subscribe to any news groups that hold a particular interest to you. Check the help files of your news reader for more specific instructions. Common courtesy is the first rule of newsgroup postings. Make sure your post is on the topic it is intended for. I've downloaded some files from the Internet.