Classes, Subclasses, Superclasses.

A Subclass inherits from a Class.

If I have a subclass B that inherits from class A,

B has all the stuff that A has.  B might also have some extra stuff as well (extra stuff:  data, methods).  But B always A's stuff and can use A's stuff.

For example, a class called Animal might have strings for genus and species.
A class called Dog might inherit from Animal, in which case it would automatically have genus and species but it might also have another variable called breed.

iOS programming is all about the classes.

UIViewController is a built-in class that controls the layout of a specific screen in your iPhone app.

We made two classes that inherit from UIViewController.  One was made by the system when we created the app in the first place, and that's called ViewController.  And the other is called Dog.

When we want to add new ViewController to our storyboard, we have to drag a new ViewController in from the Library on the storyboard.  We have to create a new piece of for that ViewController, using File-->New-->Cocoa Touch Class.  (Make sure you inheriting specifically from UIViewController.)

And, we have to, in the storyboard, indicate that the ViewController we just dragged in is of the proper subclass.