I don't have one, so this is from the linked article and my experience with a 5th gen nano. To set it up, it says...
- On your iPod nano's home screen, tap the Fitness icon.
- Tap the "i" icon in the lower rightt-hand corner to access your Fitness Settings.
- Input your height and weight (under Personal Info) and select your units of measurement and distance.
So, once you've entered your personal information, a one-time deal, when you want to do a run, on my 5th gen nano, I do the following (the first time)
main iPod screen -> Nike+iPod -> Nike+iPod ->Basic (or other workout type)
and then it tells me to walk around to activate the shoe sensor (which would not be needed in your case) and then prompts me to start my workout (press the center button).
If I want to repeat the same type of workout, it saves the options used before, so I can select
main iPod screen -> Nike+iPod -> Basic Workout