Step 1: All modern laptops will have a VGA, DVI, HDMI or DisplayPort connection that lets you add a second screen. PC users should check the back of the tower for a spare connection - if one isn't available you'll need to upgrade your graphics card. Connect the port to a matching port on the new screen.
Step 2: Click Start, Control Panel, Appearance and Personalization. Choose 'Connect an external display' from the Display menu. What's shown on your main screen will be duplicated on the second display. Select 'Extend these displays' from the 'Multiple displays' drop-down menu to expand your desktop across both monitors.
Step 3: Alternatively, you can view the desktop on just one of the screens - perhaps the larger of the two. Click the Identify button if you aren't sure which screen Windows is referring to as '1' and '2'.
Step 4: Adjust the resolution for each screen to improve the quality of text and video shown onscreen. From the Display drop-down menu, select a display and click Resolution. Use the slider to adjust the screen's resolution. It's advisable to use Windows' recommended resolution for each display.