Okay I think I know what you are asking.
You probably were looking at your SharePoint list and from here clicked 'Create PowerApp'?
That will give you 1 screen with the edit fields representing each sharepoint list column. To get the 'new form' screen, 'detail screen' and 'browse screen' you should create your app another way:
Go to PowerApps and click on '+ Create an app'.
Chose your layout (phone or tablet) and THEN connect to a datasource (your sharepoint list). This way, you will automatically get the 3 screens with all necessary controls.
If this was not what you were asking, try it anyways because it gives you a sample app where you can lookup the functions used (e.g. to create a new form).
