You do not need any additional setup action in order to start using iAd in your game. Just make sure you have your iAd Contract on action:
You can review it in iTunes Connect under the Contracts, Tax, and Banking section.
After this, you can use Plugin iAd API. The usage example can be found under iAdExample scene.
If you prefer to use the features without the code, you may use Prefab solution with can be found under iAdNoCodingExample scene. Or use Playmaker actions for iAd.