How to play songs on iPhone link with USB interface?

Need to have an AUX cable, and then find the AUX interface in the car. For the iphone4s, there is also an apple plug-to-AUX head converter with accessories. Please see the figure below for installation. 1. first connect phone4s: including adapter and AUX cable (brackets in the figure are not needed). 2. Find AUX interface in the car: (Different parking spaces are different) Some car audio panels also have USB interfaces, which can directly read the contents of the U disk. 3. Just select AUX on the sound panel.