Android Question Rewarded interstitial example

I could really need some guidance on how to set up a demo googe demo ad of a rewarded interstitial as a simple example.

Right now I got the full helper class but i'm new to this so i need something simple to start with. I have suceeded to set up a normal ad banner, but rewarded inerstitial needs callbacks for coins, cancellations, and errors,from what I gather. It gets tricky when you are not used to it.