You cannot put apps on the iPod nano.
Because of it's light weight and little clip, the nano was the choice in the fitness community, but they're quickly becoming obsolete because without GPS, wi-fi or Bluetooth, there isn't much you can do with it other than listen to music.
Basic things that millions of people do now days like mapping your run, uploading workout details and pairing to wireless speakers are impossible with the iPod Nano. It's really sad how even though technology has advanced so much, but we still have to carry our phones with us when we run or workout. Now they want us to carry a phone AND a watch.
I understand the space limitations but Apple should at least make iPod adapters that when connected, gave you Wi-Fi, Bluetooth, GPS abilities and more.