You can easily extend your Windows desktop across more than one monitor by plugging two or more monitors into a desktop computer or one or more monitors into a laptop. Most laptops allow you to connect one external monitor. A desktop that spans two or more monitors significantly increases your desktop area so that you can drag windows, program icons, and other items to any location on the extended desktop.
By default, when you connect an external monitor to a laptop, the same image (mirror image) of your desktop appears on the external monitor. Before you can drag a window from your laptop screen to the external screen, you must extend your display by changing your display settings. By contrast, when you connect another monitor to a desktop PC, the display is set to "extended" by default, and you should be able to drag a window from one screen to the other without changing any settings.
Open Screen Resolution by clicking the Start button , clicking Control Panel, and then, under Appearance and Personalization, clicking Adjust screen resolution.
Click the drop-down list next to Multiple displays, click Extend these displays, and then click OK.
If you don't see an option named Multiple displays in your display settings, then Windows isn't detecting a second monitor plugged into your desktop computer. Or, it is not detecting an external monitor plugged into your laptop. When Windows detects this monitor, it will appear in the drop-down list next to Display. If you don't see it listed there, try clicking Detect.
Make sure the monitor you want to extend your desktop to is turned on and plugged into the correct video port on your computer. You might also need to select the correct source labeled on your monitor's controls to ensure the monitor is using the correct video port. For more information, check the manual for your monitor or go to the manufacturer's website.
Click the title bar of the window, and then drag the window to a new location.