In-app ads are not intended to be used to advertise your app. It is a different way to monetize non-paying players of your game.
To get advertisement placement reward a contract is required:
This type of ads is designed to be shown on gameplay pauses like level transitions and in other similar cases. You do not need to reward a player after he has watched such an ad. But make sure you do not use this ads way too much.
Interstitial ads are available on android platform at the moment
At the moment following ads can be shown to a player while using this feature:
Feature support on other platform is currently under developement
To implement interstitial ads you need to use a single SDK method: