Get gmail Inbox Messages using the gmail API

Question

I want to get Gmail Inbox messages in my android app. So, I go to the quickstart for gmail api for Android. But there I got https://developers.google.com/gsuite/guides/android only Prerequisites and Prepare the Project.

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:25.0.1'
    compile 'com.google.android.gms:play-services-auth:15.0.1'
    compile 'pub.devrel:easypermissions:0.3.0'
    compile('com.google.api-client:google-api-client-android:1.23.0') {
        exclude group: 'org.apache.httpcomponents'
    }
    compile('com.google.apis:google-api-services-<API>-<VERSION>') {
        exclude group: 'org.apache.httpcomponents'
    }
}

After that the tutorial said : "Once the service is authenticated, executing the API call is the same as shown in any of the G Suite Java quickstarts."

So, My question is what is the next step that I can read gmail inbox messages in my android app (in Java) ?

Any help is appreciated. Because I stacked for 3 days.