When registering with AdMob, they want to see where your application is located, but this is not an important part of the process from your point of view.
Basically, for AdMob (as well as a number of other similar sites), you download a small SDK that you add to your Android application. This SDK usually has a view that you can use for one of your activities. You give this control some information, such as the AdMob private key (so that it knows who you are), and then this control will provide an advertisement from the server. Note: this usually doesn’t work right off the bat, and there is a “development mode” that you can set to always repel a fake ad while you just work on it.
You can also subscribe to several sites and check out AdWhirl, which allows you to control the ratio of ads displayed on each site, as you will find that some sites will generate more revenue for you than others.
Good luck
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