Chapter 2: Creating an iOS Application

Interface(.h) - class declaration and defines instance variables & methods
Implementation(.m) - code for the methods

@interface HWAppDelegate : UIResponder <UIApplicationDelegate>
- the class inherits from the UIResponder
- the class implements the interface from the UIApplicationDelegate, which is a list of protocols

Delegation is similar to the action connection in that one object calls methods on another object as needed.