XCode: Can't find library

Hi
I got my first mac today (macbook pro), so I'm newb to all this. I installed Xcode and watched some tutorials, and on all of them they use the library.
I've looked around but cant seem to find it, even if I do exactly as the people in the tutorials. Things I do is such as opening the Interface builder through mainwindow.xib. And well, everytime anyone opens the interface builder, library pops up. But not for me.

Thanks