i want to add an ads in my new game in unity3d 5.2 how to put the ads code ?

i want to add an ads in my new game in unity3d 5.2 , i made account in ads unity and linked my game in the service of ads and turn on the ads just they need to add the simple ads c# code to the game, the question is here ?? how i can add the code to my game (where exactly) ?? thanks