Got to EachScape Plugin Section, install AdMob Plugin.
Once you have added the AdMob plugin to your app, go your app's Configure page, click on the Plugins tab, and enter the App ID for your Android and/or iOS AdMob app. Your app ID can be found under App settings in Google's AdMob dashboard.
In order to incorporate AdMob into Google DFP use the following settings for your DFP creative:
If using custom ad sizes, the AdMob Block should be the same size as the ad it will load.
To add an AdMob banner ad to your app, drag the Google AdMob block into your app, and enter the Ad ID and the type of your ad. Ads will take a moment to appear in the app while the AdMob block talks to Google's servers.