iOS Programming: The Big Nerd Ranch Guide, 7th Edition

UINavigationController

A UINavigationController maintains an array of view controllers presenting related information in a stack. When a UIViewController is on top of the stack, its view is visible.

When you initialize an instance of UINavigationController, you give it a UIViewController. This UIViewController is added to the navigation controller’s viewControllers array and becomes the navigation controller’s root view controller. The root view controller is always on the bottom of the stack. (Note that while this view controller is referred to as the navigation controller’s “root view controller,” UINavigationController does not have a rootViewController property.)

More view controllers can be pushed on top of the UINavigationController ...