Connect multiple monitors together by connecting a new monitor to an open monitor port on the back of the existing computer. Most modern operating systems automatically detect the presence of a new monitor and adjust settings accordingly. If the operating system does not recognize the newly connected monitory, restart the computer.
If a computer does not have multiple monitor inputs, consider connecting multiple monitors together using a splitter. However, most of these splitters result in some loss of image quality. Also, if a video card does not have multiple monitor inputs, it may not be able to support multiple monitors, even while using a splitter. Contact your computer's manufacturer if you are unsure of your computer's video capabilities.
If you have an appropriate video card, you can manually adjust the settings for multiple monitors within the card's settings application. The exact procedure for doing so varies between video card models and manufacturers.
Older operating systems, such as Windows XP, do not automatically detect multiple monitors. For Windows XP, navigate to the Display Settings tab via Appearance and Themes from the Control Panel. Activate other monitors by right clicking the blank monitor and selecting "Extend my Windows desktop onto this monitor." This activates the other monitor, but you may have to adjust resolution settings to get an acceptable picture.
Using multiple monitors on even older operating systems is a challenge, and doing so typically requires using third-party software.