If your car doesn't support CarPlay, you can't find the CarPlay receiver you want, or what you have doesn't support it very well, you can create a reasonable facsimile on your iPhone or iPad. Here's how.
Back in the day, you could use iTrip to broadcast on FM from your iPod to your car radio. Now there's CarPlay, which is just about infinitely better — but only if you have it.
If your car does not support CarPlay or, startlingly commonly, if the way it supports it is just so very poor and un-Apple-like, there are things you can do. You can make your own CarPlay control using your iPhone or iPad, and either a windscreen or car vent mount.