Hey There i am developing a 4 screen app in which i want to show banner ads in my login page and my main screen and in my 3rd screen can anyone here help me with the full process. the app will also be published on google play and app store.
It seems you have just created a new account. You told us you were using Niotron. Show that you are using App Inventor. Until then I unlist this.
You can not use extensions when making an iOS app. It seems you have some reading to do. I never help with adding ads and it seems you are making a kind of earning app. Another reason not to help. Maybe some one else is willing to do that.
Both distribution methods have very specific requirements regarding ads in an app. Have you read the Google and Apple guidelines for developer's use of in app ads? They have requirements.
You might find the very simple, primitive, free, native Block method useful to provide an ad without requiring an extension. 
Here are some resources to help you learn to use the AI2 tools. A very good way to learn App Inventor is to read the free Inventor's Manual here in the AI2 free online eBook http://www.appinventor.org/book2...the links are at the bottom of the Webpage. The book 'teaches' users how to program with AI 2blocks.
There is a free programming course here Course In A Box and the aia files for the projects in the book are here: App Inventor 2 Book: Create Your Own Android Apps
How to do a lot of basic things with App Inventor are described here: How do you...? .
Also look here http://kio4.com/appinventor/index.htmandherehttp://www.imagnity.com/tutorial-index/ for more tutorials.
Otherwise you have to make your own extension which will only work w.r.t . Android projects. 
all done now what to do im confused???
Sorry did not know it was a crime here to ask someone to be nice and not do things as irrelevant as your comment
Watch2Earn or Click2Earn apps violate Google AdMob policies, which prohibit artificial engagement. This discussion is not suited here.