To take advantage of the new features you'll need to navigate to the Android Auto page on the Google Play Store and manually update the app from there. Google is updating the system with new features to make it even faster to find music and check messages. The album art views, for example, are an important change that will let you quickly identify different things you can play and start playback without much hassle.
Android Auto is receiving a number of promising new features, including wireless connectivity, group messaging, and Google Assistant built-in. Now when you search using your voice it will not automatically play its result but will give you other options for what it has found under those search parameters - categorised as well. Play Music is the one I subscribe to and so it's what I used for testing, and while the new media updates do make it quicker to pick from Recents, you sadly still can't browse artists or albums. With Prime, you get Prime Music for free, meaning you have on-demand access to 50 million songs, all ad free.
The new search features were something that escaped us yesterday but Google have outlined the improvements they have made to the voice search capabilities. In many cases this removes multiple taps from the media search experience, which is critical in the auto. For example, you'll now be able to read text messages (as well as group MMS and RCS) through your vehicle's display, but only when stationary.
Why buy a finished Android Auto head unit when you can hack one together with a Raspberry Pi 3? Google says that this update is rolling out today and should be fully available to everyone over the next several days, so keep an eye out for it.