How to use photoshop graphic files (*.psd?) in xcode?

I heard that I can directly import photoshop psd file into a XCode project to use the images provided by the psd file. However, i could not find a way to impor开发者_如何学运维t the psd file into the interface builder. Can some expert help me out here? How do i make use of a psd file? Or what is the another file format i need to use? thanks!