It's my first time using unity ads,how can i show advertisement when the player kill the boss?

Of course i have no amount of advertisement in my app,but i want to learn how implement it to implement after.
When the player kill the boss show the ads ,verify if the member close or the ads finished and when it's happend call a void that calls an Application.LoadLevel ("level here");
if somebody can give me a sample of code i'm really appreciated.
Thanks in advanced!