Neither. Nike+ is a sensor and receiver for the iPod Nano or iPod Touch. If you have an iPhone instead, the receiver is built in so you only need the sensor. Nike, of course, wants you to buy their “special” shoes that have a compartment in the sole in which to put the sensor. But really, you can go to Amazon and search for “nike+ pouch” and you’ll find a bunch of little pouches for under $10 that you can just tie onto your laces, and they work just as well. No reason to fork over more money to Nike for special shoes.
You stick the sensor in your shoe, connect the receiver to the iPod, and go to “Nike+ Ipod” on the menu. You select what kind of workout you want (basic, time, distance, calories), and whatever goal you’re looking for, then you select an album or playlist you want to play while you’re running. Then you start running. As you go, every so often it will automatically tell you how you’re doing. For example, if you choose a 5K distance workout, it will tell you when you reach 1K, 2K, 2.5K, etc. If you choose a 30 minute time work out, it will tell you at 10 minutes, 15 minutes, etc. Or you can push the center button while it’s playing and the music will fade to background as the voice tells you your current time, distance, and pace.
When you’re done, you plug the iPod into your computer like normal, and iTunes transmits your workout data to your account on Nikeplus.com, where you can keep track of all your runs.