This screen is the TV version of YouTube's interface running in the internal web browser. It is more keyboard and remote control friendly than the regular web interface. If you have a YouTube or Google account you should log-in so you can get customised recommendations based on your viewing habits and you can also see the channels you subscribe to.
There is a quirk of the YouTubeTV interface that when you press ESCAPE it will ask you do you want to exit but it doesn't work. For now you can press RED (F1) to exit the screen