If you already have, or are thinking of getting, an external monitor to give you more real-estate for your Chromebook then you are at the right place.
Click here for the Google Support page that explains how to hook up to a monitor or TV with a variety of connection types.
Click here to see a video from ChromeUnboxed team that demonstrates the capabilities of a USB Type C Mulit-monitor Dock using a variety of differently powered devices.
Click here for a HowToGeek article called "How to Turn off a Chromebook Screen When Connected to an External Display" if you only want to have an HDMI, or Chromecast, connected screen to be operating without your Chromebook's screen being active.