fb.gg is the official app from Facebook Gaming, that lets you watch other players' live streams, or even stream your own videos. The way it works is similar to other platforms like Twitch or Mixer (for just two examples).
From the main tab in fb.gg, you can take a quick look at all the most popular streams of the moment and join in on any of them with just a tap. You can watch them live, leave comments, interact with other app users, etc. Plus, whenever one of your favorite 'streamers' starts a new video, you'll get a notification.
One of the coolest things about fb.gg is that it offers a ton of games for you to play directly from the app. Helix Jump, Uno, Cookie Crush, Solitaire, Words With Friends, 8 Ball Pool, Chess, Quiz Planet ... the list goes on and on.
fb.gg is an interesting app that lets you watch live streams and gameplay videos for hundreds of games, both for Android and Windows. And of course, you can also broadcast your own content easily.