Messages may be commentaries, questions, or response to previous postings. In moderated newsgroups, someone screens the messages and then posts the suitable ones. Long time ago, these newsgroups were intended to be virtual places where people could exchange scientific ideas. One final point, the FAQ's get created in a group when many novices subscribe to the newsgroup and ask the same annoying questions. People just post messages which can be read by others live.
People can argue out their differences right on the spot.
If you want to experience IRC, stop by my office. The difference is that the purpose of these protocols is not necessarily to allow the visitor to leave a message but to read and hear what the host has to say. So, if I want to find out what Ms. Hawkeye has to say, I'll visit her home page. If we have something to tell others, we set up our own home page and let people accidentally or deliberately read our home page. In a home page one can create hyper text links which can be used to jump to other home pages, and so on.