Who can watch my games?
You decide. The first time a friend asks to watch your game you'll be presented with the broadcast privacy settings...
If you select "Anyone can watch my games" then your broadcast will be visible on that game hub.
How do I start & stop my broadcast?
When you're playing a game and someone starts watching, you automatically start broadcasting. When you end the game your broadcast ends.
Try it now
To try out Broadcasting now, both you and your friends need to opt into the Steam Client Beta. In the Steam client main menu, select Settings > Account and change your "Beta Participation" to "Steam Beta Update".