Nothing to hand in (but do this!)
vi (pronounced VEE-EYE) dates back to 1976, and has been my editor of choice since 1980. Its modern versions are often referred to as "vim" (for "vi improved", pronounced VIM). There are tons of tutorials, including a vim-learning game, a kind of gamelike tutorial, and lots of short introductions.
When you're working in a Unix command-line environment, it doesn't take long for you to find yourself confronted by editing in vi, sometimes by accident, because it's often the default editor used by other programs. Even just knowing how to recognize that you're in vi, and how to save and quit, will help you out of some unexpected situations. Of course, once you get the hang of it, vi is also extremely powerful and extremely convenient.