Among the best tools for understanding these concepts that I have found and shown to many classes of students is the following video from the Stanford Law School Center for Internet and Society.
Professor Eric Faden of Bucknell University created this humorous, yet informative, review of copyright principles delivered through the words of the very folks we can thank for nearly endless copyright terms.
22 November 2011, Original Pedantic Political Ponderings post.
18 December 2011, FollowUp 1.
20 January 2012, FollowUp 2.