The Hyundai interface comes on when the car is started, with the choice to open Android Auto presented once the phone is plugged in. The Hyundai interface works with Android Auto, so that if music is playing through the car's head unit, it will continue to play in Android Auto and you can control it through the head unit. It will only switch over once you choose media from your phone. You can also use the in-car navigation while inside Android Auto - you don't have to use Google.
The Google Now home screen is what comes up first, and can be returned to by pressing the round, center icon at the bottom of the screen. It is a combination of notifications concerning what you're doing now, where you've been, and where Google thinks you might want to go, based on past behavior.
Google Maps, accessed by pressing the left, arrow button at the bottom of the screen. Voice recognition is quite good, and you can press the microphone button on the steering wheel to enter a destination by voice. If for some reason the system doesn't understand, you can enter an address via a keypad, or switch back to Hyundai navigation and try by voice or keypad there. You can use Hyundai navigation while still using Android Auto for media and phone calls, for instance.
Google Maps offers these three menu options to make searches easier, and you can use these with taps on the screen. You might know that one of the suggested destination is where you want to go, for example.
Do that from the Phone screen and you'll get these options. When you call your voicemail, if you need to enter a password, you can do that on the screen. At the top is a notification from the media player, which lets me know that a new 'track' has come up on NPR One. Notifications from other parts of Android Auto always appear at the top.
Three of the media apps available on Android Auto. At the time of writing there are 16 apps available, others will come online as they are approved specifically for Android Auto (they can't just be Android apps).
Media apps will have a similar interface, with prominent track information above and a menu bar that changes by color at the bottom, with the relevant controls. Because this is a podcast, for instance, I can go back 15 seconds using the button to the left of the big blue Play/Pause button.
Google Play has an orange Play/Pause button. At the top is a notification that I have a text message from Vincent Vega. If I tap it, the system will read the message to me - including emoticons - and I can reply by saying, "Reply," and speaking my message to the system.
The far right button at the bottom takes you back to the car's native interface. Switching back and forth doesn't change anything that's happening in the system until you actually request some sort of change.
In addition to voice text messaging, the Motorola Moto360 watch was a surprise favorite. It's a phone on your wrist, connected to the phone and therefore the car, and fills in every blank you might encounter. You can use it to send text messages, set reminders, lock and unlock and start the car remotely, and if you need a larger screen you can port its information to the phone or the car head unit. It's a winner in my book.
Once you plug your phone into the USB drive, the handset is blacked-out with this screen. You are almost entirely locked out of the phone, but that's the point of the system - to keep the handset out of your hands.