main.m
-Basically just the C entry point function int main(int argc, char *argv[])
-Creates an autorelease pool
-Calls UIApplicationMain which creates a UIApplication object and starts the run loop

MainWindow.xib
-Contains a UIWindow (top of the view hierarchy) for things to be installed in
-Can be (usually is) customizable per platform
-Contains the Appliation Delegate (just an NSObject which its class set to YourAppDelegate)
-Application Delegate also has a couple of outlets wired up (notably to YourAppViewController)

YourApp-Info.plist
-A variety of application configuration properties

YourAppViewController.m & .h & .xib
-Has an instance variable for the UIWindow in MainWindow.xib called window
-Has an instance variable for YourAppViewController called viewController
-Has stubs for a lot of applicationDidxxx and applicationWillxxxx
-Most importantly application:didFinishLaunchingWithOptions:
     This is the method where YourAppViewController’s view is added to the UIWindow
     Also where the UIWindow is made visible [window makeKeyAndVisible]