How do I enable Apple CarPlay in my Audi A4?

I recently purchased an Audi A4 and I want to use Apple CarPlay in my car. How can I enable it?

To enable Apple CarPlay in your Audi A4, you will need to have the optional Audi smartphone interface package. If you have this package, you can simply connect your iPhone to the USB port and then go to your Audi's menu and select 'CarPlay' as your source. If you do not have the Audi smartphone interface package, you can purchase it from your local Audi dealership.