What is adaptive banner?
Adaptive banners are the next generation of responsive ads, maximizing performance by optimizing ad size for each device. Improving on smart banners, which only supported fixed heights, adaptive banners let developers specify the ad-width and use this to determine the optimal ad size.
How do I add a banner in AdMob?
Click Create ad unit. Follow the Google Developers instructions for Android, iOS, or Unity to implement banner ad units in your app code. You will need your app ID and ad unit ID during implementation. This ad unit won't show ads until you've completed this step.