There are a few steps that you have to take before creating app which uses Google Maps API:
- creating Google API project in Google APIs Console (https://code.google.com/apis/console)
- enabling Google Maps API for Android (in the Services tab)
- creating new Client ID (you should enter SHA1 key and your's app package name)
Have you done all of that? If yes, please provide logcat output which contains information concerning authorization failure.