Can't get ads in my Android app

I'm getting problems trying to add adverts to my app, I'm not a good coder in fact I hardly know how to code and I've tried many freely provided assets hat help add adverts but the furthest I got to having ads was from this.. https://code.google.com/p/google-mobile-dev/downloads/detail?name=UnityPlugin_Android_1.0.zip

I managed to get a banner show on my Android using the demo script but as soon as I do the necessary changes to the android manifest the banner disappears and no ads appear at all,

I'm not sure whether it's to do with my app or the link to admob account? I'm really confused, If I can't do it myself what's the best on the asset store to help me?