Unfortunately most radios don't support music from an Android (or any non-iPhone for that matter) through USB. They have Apple's proprietary protocol to do that for iDevices, but for any other one, the USB port will only work as a media storage device (so you'd only be able to play local files, just as if you were using an USB stick or old MP3 player). For this to work, though, your phone's USB mode should be set to USB Storage.
Another option is to plug it in through the AUX IN port in your radio (if available) to the phone's Headphone jack. Or use Bluetooth or if your car doesn't have any of those, purchase a BT radio transmitter. Basically your phone connects to the transmitter through BT, then that broadcast the signal to a generic FM radio station.