It seems like something that should’ve existed from the start but it hasn’t—until today, that is. Google has just started rolling out a favourites feature. This means, you can just tap a star on the upper right corner of your photo of choice and this will then show up in your Favourites. The album will self-generate when you start starring photos. It may or may not be showing up for you yet. If you don’t see the star option, then it hasn’t landed yet. Google is also planning to let users “heart” photos that have been shared with them, adding a bit of a social component to the app.
Source: The Verge