Most modern laptops are automatically equipped to connect an external monitor in addition to the laptop's own LCD. This is because many laptops are often used for storing and showing presentations, and it just makes sense to have the laptop all ready to go in that respect.
To add the external monitor, locate the monitor connector on your PC's rump. Plug in the monitor, and you're ready to go. You can use that monitor in conjunction with your laptop's LCD or as your laptop's only display.
On some laptops, the same image appears on both the LCD and the external monitor.
If you want to use the external monitor exclusively, just close your laptop's lid. Most laptops are smart enough to see the external monitor and let you start using it, and also keep the laptop's power on while the lid is closed. When you open the laptop's lid, control returns to the laptop's LCD.
Note that if you close the lid, it helps to have an external mouse or keyboard connected to the laptop so that you can still use your software.
To activate the external monitor, you may have to press a special key or key combination on your laptop's keyboard.
The monitor connector can also be an S-video connector. It allows you to connect your laptop to not only an external monitor but also many TV sets, VCRs, and DVD players.