What's the MainWindow.xib nib file for?

I am new to iOS developement, and i am trying to understand the whole cycle of iOS application developement, and i feel there's a missing part i just don't get it..

if the MainWindow.xib that is generated automatically by Xcode has a view that loads another xib/ni开发者_JS百科b view inside it, then why we use it ?

Your application needs a window so the system can display it to you on the device screen. In the window are various views which represent different areas of your application that users can interact with. Views can either be entire user interfaces, or individual UI controls.

The main window interacts with your application delegate to handle events that your application receives through the views.