Once connected, Android Auto will automatically project your phone to your vehicle screen. You'll be notified that Android Auto will turn on Bluetooth, pair your phone, and sync your contacts. Unless you have opted out, just tap Continue. 

Then you can access your apps. If wireless connection isn't available the first time you try it, you can also connect by plugging your phone's USB cable into your vehicle's USB port to enable wireless connection.

In the future, Android Auto should launch automatically. But if not, tap the icon on the vehicle infotainment screen. Talk to Google and get things done with your voice so you can keep your focus on driving easily, send messages, get directions, control media, and more.