How to listen to music from my iPhone 4 with the bluetooth in car?

Thanks

Your need a bluetooth headphone like this one
http://www.amazon.co.uk/...B00ISG8QDG

Your question is not very clear.

If you want to listen to music through car speakers?

Then you need to make sure first that your car is capable of pairing with a Bluetooth device.

If yes- then go to settings or Bluetooth settings and then click pair- (same time go into iphone Bluetooth settings and make the device visible so the car can see the device) - after that follow the instructions shown on the iphone or the car's system.

If you do not have a system that would recognize Bluetooth then you just can't - unless you buy a device that would transmit a frequency with which iPhone can connect and which in turn would connect with the car via a wire and then listen to it.

For an answer to the second part we would need plethora of details.