To add the NSObject:
Select the .xib file. In View > Utilities > Object Library, search for an NSObject (using the search box at the very bottom), and drag the Object to the Objects section of the gutter (or whatever you want to call the thing that lists the contents of the .xib).
To change the custom class:
Select the new NSObject, then View > Utilities > Identity Inspector. In the Custom Class section at the top, change the class to QuizAppDelegate.
For the monkey feeling (which I’m guessing a lot of people get initially; I did as well), the important thing is that your brain gets used to the pattern and relays this to your fingers, so after awhile you’re like “Yeah, yeah; create the IBOutlets, create and synthesize the properties, add the IBActions, make the connections…I could do this in my sleep.” That’s the point of actually doing it.
You COULD just copy-and-paste the code from the solution code, or worse, just sit back in your easy chair and read the book with no hands-on time. After all, it would mostly make sense. But then when you sat down to actually create your own app, you’d be lucky to get even the initial Quiz app working without going back to the book.