In App Building Tutorial

1.) Add permission to app Manifest file
<uses-permission android:name="com.android.vending.BILLING" />

2.) Create billing Package in app
Call it com.android.vending.billing and make sure its at /src level, not within your other package

3.) Place IInAppBillingService.aidl file in billing Package
This file is called IInAppBillingService.aidl, downloadable through SDK manager under Extras, and is located in your SDK folder (for me, it was here: \AppData\Local\Android\android-sdk\extras\google\play_billing and you can drag it right into the package in Eclipse)

4.) Create billing utils Package in app
Call it com.android.vending.billing and make sure its at /src level, not within your other packages

5.) Copy all files from the Android TrivialDrive sample app into billing Utils package to help us implement billing
Nine .java files, Base64.java through SkuDetails.java, located in a subfolder of Step 3's folder.

6.) Make a button in your app that will allow the user to buy something!

7.) Get your public license key from the App's page in your Developer's Console. It's a long Base64-encoded RSA public key.

8.) Code using those borrowed utils! Examples to follow