The "Google Camera" application named has been updated to feature a selfie flash which is usually missing from the front cameras of most smartphones. Obviously, the United States is one of them. Google has noted that the version is created to work on recent Nexus and Pixel devices running Android 7.1.1 and above. As for how the process works, it's as simple as the name of the feature implies.
To enable the selfie flash, tap on the Flash icon when in front-facing camera mode and select automatic or on. These features are part of the 4.4 version of the Google Camera so if you aren't sure if the update has been applied, as it could have happened automatically if you have this setting enabled, then all you will need to do is check the version number to be sure.
Those that like to zoom in while taking a photo will appreciate the newly added double tap to zoom feature that will ramp up the zoom by 50% in an instant. If you aren't keen on the new camera and video buttons, you can still use the old gesture of swiping left and right to activate and deactivate the video mode.