Don't press it unless you really want to resign. Clicking this will leave the game. Click this after the game has ended to go over the game with your opponent. At the very bottom are the window where comments can be seen. Players will only see comments made by other players.
Observers see everybody's comments.
Below that is the field where you can enter your own comments. To the right is a list of people in the game. If you are editing the game, you can give somebody else editing control by right-clicking on their name.