Close Chat nodes are storyboard elements that identify the end of a bot path. These tell the Instabot widget to close automatically when the user's conversation is over.
This is not required, but it is good practice so that the Instabot widget is not left open on your website after they have completed your Instabot conversation.
A Close Chat button exists at the end of each bot path on the storyboard. Select this button and you will see the element added to the storyboard.