You can find a factory car radio diagram in your car owner’s manual. Or, if you look in the packet of information you received with your new car, it is likely you have received information about the radio options you have purchased. Indeed, that information should have been provided to you. It will describe not only the radio options you have purchased, but also information about the radio itself, including a diagram of the radio. In case you have lost the manual, you can search for it online on the manufacturer’s website as well.
For more info, see Replacing Your Car’s Factory Radio