This is from my VERY limited experience with it, so YMMV.So work with me here and outline exactly what this new stuff on the information highway does that email and a cell phone will not do. Talk slow and do not use big words.
FB allows you to have "friends". In your account you have a "wall", and when you post something there, anyone who is your friend instantly gets a notification of that post.
So, it's a very quick way of disseminating information to "interested" people. You can alternately send a private type of message too, if you want to, but the intended use is to simply type a message, add a photo or two, and then everyone who cares, instantly knows about it, and can view said items.
A similar concept to friends is "fans". I don't know exactly how they differ, but I believe the same concept applies, that when you post, your "fans" get it. I've only known of celebrities or businesses who have "fans", rather than friends.
By being a "friend" or a "fan" of someone, you are in essence saying, "I want to be kept informed of what you want to post". From there it's automatic, both for me as a poster, or as a friend of someone else.
Ray