Programming style

Hi all, I am writing here because I can't catch the right programming style when using both Xcode and the interface builder. Everything in an interface is not static (for example, lists in a view can change or update, or can be deleted or created), so I can't understand why is useful to design an interface while it will be created during code development.
I'm a newbie with this stuff; I just need an overview about common things to do when creating a cocoa application.

Thank you, and I apologize for bad English.
—Albe