Randy Cassingham has an excellent Spam Primer online: Getting Rid of “Spam” and Other E-mail Pests. The basics of spam, “phishing” and other e-mail pests, how they got your address in the first place — and what to do now that you’re inundated.
This is very comprehensive and may be a bit daunting at first if the subject’s new to you, so you may prefer to start with the one-page basic version. If even that’s too much then you can read The Very Basics — a 6 point summary on the right, near the top of that page.
And do someone a favour by telling them about the Spam Primer. You may save them a lot of anguish.