Hi all.
I would suggest updating Admob tutorial - unfortunately it says nothing about you being unable to preview ads until you will build app. I have just spent 1,5 hour fiddling and looking for error on my end until I asked around, checked forums and found few people saying you cant do this and they have also spend a lot of time thinking it was their error, not the fact you need to export app with Intel XDK before you can see even test ads (not sure why test mode exist then...).
Making this clear would save a lot of time to many people that use Admob plugin first time.