Now that the model is taken care of, we turn to the other end of the application: the views. Our design for the application relies on standard elements in the Mac OS X Aqua interface.
Interface Builder (IB) is the indispensible tool for laying out human interfaces for Mac OS X applications. It edits Nib files, which are archives of human-interface objects that are reconstituted by your application when the files are loaded. All Cocoa application have a main Nib file, which the Xcode application template names
Main-Menu.nib. This file contains at least the main menu bar for the application and may contain other applicationwide windows and views.
An application can have more than one Nib, and a Nib can be loaded ...