This is my first experience of Power APP. WhenI press play button I am being directed back to the list of all the apps it does not display the Page that I am trying to test

This is my first experience of Power APP. WhenI press play button I am being directed back to the list of all the apps it does not display the Page that I am trying to test
It sounds like you are using the Play option that is in the list of apps. I recommend you test from within the editor, not from choosing Play from the list of apps. Simply go to the starting page of your app and select the play button from there. Depending on what you have the first screen doing, I would expect it to render your Screen1 or equivalent and be waiting for you to take some action, but that will entirely depend on what your app does.