In short: After many years of resisting Android Auto and Google, Toyota has announced that it will begin adding Android Auto to its vehicles. The Japanese car maker did not mention when Android Auto would be available, or which model years would get it. All we know is that Toyota is finally going to add Android Auto, which is still a pretty big deal. Toyota has had Apple CarPlay available on its vehicles for a little over a year, but that was after Apple beat the resisting side of Toyota.
Background: Toyota had resisted adding Apple CarPlay and Android Auto to its vehicles because it felt like they were handing the keys over to those companies. And the reason why that was a big deal to Toyota was because both companies were working on self-driving cars, and Toyota saw them as competitors. Now both are still working on self-driving cars - though Google is working more on the software side, and using existing vehicles for the hardware. Toyota likely is making sure that Google can only gather certain information from Android Auto, on its vehicles, as that was Toyota's biggest issue with not allowing Android Auto in the first place.
Impact: This means that those that own a Toyota vehicle will be able to use Android Auto in the near future. Instead of just mounting their phone to use Android Auto on their phone, they'll be able to plug it in and use the screen that is built into the car for Android Auto, which does provide a much better experience than just using your smartphone - because the vehicles typically have a larger display. Hopefully Toyota will soon announce which vehicles will be getting Android Auto support, but it will likely include the Corolla which is one of the company's best-selling vehicles (also one of the best-selling vehicles in the US, across all automakers).