Although modern laptop screen sizes are getting bigger every year, their desktop cousins are still much larger. Tasks like viewing large spreadsheets, video editing or just watching a movie are accomplished much more comfortably on a large monitor. Every laptop in the past decade has some type of video output, designed to connect it to an external monitor. The most common of these outputs is an "RGB" (or VGA) output. Although incapable of displaying HD content, an RGB connection is perfectly acceptable for any non-HD task for which you may need to use an external monitor.
Power on your laptop. Connect the VGA cable to the laptop's output. The output is usually located on the side of the laptop's chassis, but it may be in the rear. If there are nuts to which to tighten the VGA cable's connecting screws, hand-tighten them until they are firmly connected.
Power on your external monitor, and connect the other end of the VGA cable to the proper port on the monitor. Hand tighten the connecting screws down until they hold the cable firmly in place. Cycle through the display modes on the monitor until you see your laptop's output. Every monitor has different methods of cycling, so consult your owner's manual for specific instructions.
If your laptop's output is not appearing on the monitor, and the monitor is in the proper display mode, you may have to close the lid or enable external display in the display settings. These can usually be accessed by right clicking on your desktop and selecting "Properties." Locate a setting that enables external output. Every laptop is different in this regard, so consult your owner's manual for specific instructions.