Hey there cerissa75,
Thanks for reaching out to the Apple Support Communities. To get started, it may be expected behavior for music to autoplay when connecting your iPhone to a Bluetooth or USB accessory such as a car stereo.
While there isn't a setting to disable this on your iPhone, some car stereos may have the option to disable this in the stereo settings. For the best information on if this setting is available for your stereo, we'd recommend reaching out to your car manufacturer.
We hope that's able to help.
Have a great day!