Public Alerts are integrated into Google Search. If you search for a place where there is an alert active, or from within an affected area, you’ll see a warning like the one above, and can click through to find out more information.
You’ll also see Public Alerts in Google Maps. If you’re searching Maps on desktop or mobile you’ll get alerts for that area, and if you’re using the Google Maps for Mobile app you’ll see a warning notification if there is an alert nearby.
Google Now on Android is also integrated with Public Alerts, so that if there’s an alert active for your local area you’ll receive a notification letting you know what’s going on, and showing you the affected area.