In the project navigator, select MainWindowController.xib to open it. (If you double-click the file, it will open in a separate window. Close that window and single-click the file to see it in the editor area.)
Selecting MainWindowController.xib opens it in the Interface Builder editor, a tool that is part of Xcode. With Interface Builder, you can create an application’s user interface visually rather than in code.
Interface Builder has two main sections: the dock and the canvas. The dock, on the left, lists the objects in the XIB in the document outline view (Figure 1.10).
Figure 1.10 Interface Builder layout
If you see a stack of icons in the dock rather than a list ...