To set up a GCM account go to Settings -> E-mail accounts and click on the “Create account’ button.
Then you can configure:
Account name: internal account name in the system, used mainly for its identification
Sender ID: enter Project Number which is found in the Overview tab of our project on the Google Developers Console: https://console.developers.google.com
Api KEY: Api KEY from Google Developers Console, available at: Apis & Auth -> Credentials.
GCM server: choose a server from the GCM.