In the developer console go to API Manager
Fist you will need some some API Keys.
- Go to Credentials.
- Select Create credentials and choose "API key" and "Android key".
- In the next screen put any name for your credential.
- In the +Add package name fingerprint write your package name (com.sourcey.materialwhatever) and the fingerprint that appears in your log (E4:...:B9).

Now from the API Manager go to Overview
- Look for "Google Maps Android API" and enable it.

You probably got a debug keystore when you installed android sdk, with it you could check your fingerprint using the command:
($HOME/.android/debug.keystore is the default location)
keytool -list -v -keystore .android/debug.keystore
http://developer.android.com/intl/es/tools/publishing/app-signing.html