GcmBroadcastReceiver - GcmListenerService - google-cloud-messaging

Question

Could someone explain to me how the GCM receiver works in the following example. By setting at
gcm_receiver name = "com.google.android.gms.gcm.GcmReceiver"
and in category my package what do I achieve? Does it mean that GCM messages are received from GCM receiver (without writing any code) and delivered to my app, where my GCM listener receives them?
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="gcm.play.android.samples.com.gcmquickstart" >
<uses-permission android:name="android.permission.INTERNET" />
<!-- [START gcm_permission] -->
<permission android:name="gcm.play.android.samples.com.gcmquickstart.permission.C2D_MESSAGE"
android:protectionLevel="signature" />
<uses-permission android:name="gcm.play.android.samples.com.gcmquickstart.permission.C2D_MESSAGE" />
<!-- [END gcm_permission] -->
<application
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:theme="#style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="#string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<!-- [START gcm_receiver] -->
<receiver
android:name="com.google.android.gms.gcm.GcmReceiver"
android:exported="true"
android:permission="com.google.android.c2dm.permission.SEND" >
<intent-filter>
<action android:name="com.google.android.c2dm.intent.RECEIVE" />
<category android:name="gcm.play.android.samples.com.gcmquickstart" />
</intent-filter>
</receiver>
<!-- [END gcm_receiver] -->
<!-- [START gcm_listener] -->
<service
android:name="gcm.play.android.samples.com.gcmquickstart.MyGcmListenerService"
android:exported="false" >
<intent-filter>
<action android:name="com.google.android.c2dm.intent.RECEIVE" />
</intent-filter>
</service>
<!-- [END gcm_listener] -->
<!-- [START instanceId_listener] -->
<service
android:name="gcm.play.android.samples.com.gcmquickstart.MyInstanceIDListenerService"
android:exported="false">
<intent-filter>
<action android:name="com.google.android.gms.iid.InstanceID"/>
</intent-filter>
</service>
<!-- [END instanceId_listener] -->
<service
android:name=".RegistrationIntentService"
android:exported="false">
</service>
</application>
</manifest>

Answer 1

From com.google.android.gms.gcm, GcmReceiver was described as WakefulBroadcastReceiver that receives GCM messages and delivers them to an application-specific GcmListenerService subclass.
Likewise, as also discussed in Set up a GCM Client App on Android, in editing your application's Manifest:
GcmReceiver handles messages sent from GCM to your application.
GcmListenerService enables various aspects of handling messages such as detecting different downstream message types, determining upstream send status, and automatically displaying simple notifications on the app’s behalf.
InstanceIDListenerService handles the creation, rotation, and updating of registration tokens.
Checking the documentation will help you to understand how GCM Client App works on Android.