If you are an Android developer with creativity, you can earn some money by creating apps and hosting it at Google’s Android Play store. Yeah! Many developers are creating apps and earning descend money with them. This is why 60% of apps are free on playstore and many other app stores.
Will they give money for just creating an app or using an app? definitely NO!. But you can serve some ads provided by Google Adsense or other advertisement networks [ I suggest Google Adsense] with you free apps. If any of your user [users of your app] clicks on them, you will get some money.
You need to create an account on Google Adsense. That means you need to signup for adsense program with your gmail id and requires their approval.
You can signup adsense by: http://adsense.google.com but this must be your final step because you need a nice blog/website/app with strong visitors or users and then only you will be accepted.
For creating an account on Google Play store, need to pay $25 as onetime fee. [ Adsense account is free of cost, if you don’t have app, you can use it for blogs/websites also].