STEP 1: CREATE build.gradle FILE
In Eclipse select your project, then go to File, Export.
Select Android, Generate Gradle build files, Next, Next, Select your project, Next (do not force override of existing files), Finish.
Now you should have a build.gradle file in your app root folder.

Now edit build.gradle, you need to add Google Play Services dependency (at the moment 5.+).

dependencies {
compile fileTree(dir: 'libs', include: '*.jar')
compile 'com.google.android.gms:play-services:5.+'
}