How do you use your iPod shuffle or nano?
Nanos or shuffles are great for workouts at the gym or while running. You can use them just about anywhere. I personally use a Classic for my stuff, but the nano is great if you have a smaller library or want something very mobile.

As far as what you can do with it (other than playing music), it really depends on which generation you have. You obviously can't really run 'apps' on it, but many generations (of nanos) had some small games, radios, could play video, etc.