Q:

How Google Cloud Messaging Service in Android Works?

I want to use GCM Service in my application.
I have referred to the following link (Android Developer: Google GCM) but was not able to install the GCM Library in my eclipse. 
From the SDK manager I am not getting GCM Library in the Extras Folder.
Can anyone please help me?

A:

I had similar issues and it was resolved once I updated Android SDK Tools to revision 20 and Android Platform SDK Tools to revision 12. Rev 19/11 would not shown up Extras > Google Cloud Messaging for Android Library in SDK Manager.  And make sure that you restart SDK manager after updating. 
It should then show up in SDK manager as shown bellow:

