Using ads in android apps?

I have been researching how to add ads to my android app. I am a bit confused. I have added the info in the project settings for the app id and the ad unit ids. But, how do I create the ad itself? I have the graphics for the ads created already, but can’t find any documentation on how to implement them to be used in each ad.

The AdMob service is supported for Android. The Unit IDs are from AdMob; you don’t create your own ads.

I noticed that this only allows me to use banner ads. How do I do interstitial ads?

Banner, Interstitial, Rewarded Video