In IOS, you use windows and views to present your application's content on the screen.
The UIWindow class defines objects (known as windows ) that manage and coordinate the windows an application displays on the screen.
Windows do not have any visible content themselves but provide a basic container for your application’s views
The UIView
*The use of Core Animation layer objects has important implications for performance. the actual drawing code of a view is callled as little as possilble.
Tagging View for Future Identification
The UIView class contains a tag property that you can use to tag individual view objects with an integer value. You can use tags to uniquely identify views inside your view hierarchy and to perform searches for those views at runtime. (Tag-based searches are faster than iterating the view hierarchy yourself.)