You can connect your Chromebook to a monitor or TV with an available HDMI, DisplayPort, DVI, or VGA port. The instructions included with your Chromebook will tell you what type of adapter you need.
After you connect, you can:
Extend your desktop to display across multiple screens
Mirror your display to show the same image on your Chromebook and separate monitor
Adjust, rotate, and align your screen
To adjust your external display:
Click the status area, where your account picture appears.
Click the external display section > Manage displays.
From here, you can identify displays or adjust their location.
Mirror the display by pressing Ctrl and 
Rotate the image by using the dropdown menu to rotate the image on your separate monitor.
Center your screen:
Click TV alignment.
Move the viewing area by using the arrow and shift keys until your screen is aligned.
Show the display across multiple screens: Check the box for Enable Unified Desktop mode.