AdMob is a Google item that encourages you in keeping Ads on a mobile network, that permits you to monetize your Android application.
By integrating AdMob into your app you can start handsome earning instantly. If you have published a free app then definitely AdMob is the ideal option to earn income from your apps or games.
To make an AdMob account search AdMob in google and signup with your Gmail account or you can click here to sign up for an AdMob account.