iRay turns your iPhone/iPod touch into a mobile xray device to impress your friends. OK actually this application is only a mobile trick and as your device can't generate any X-radiation no one will get harmed but your friends will be still impressed.
You can control the movement of the xray picture of a right hand by slightly tilting your device. Now move your device above the victims hand (you can use your own hand if you want) following the picture on the screen. But remember: as for any magic trick you have to practice and you have to think of a story to sell it!