tell us a little more about your hardware and your Operating system.
If you have a spare video socket (i.e. your card supports two monitors) it is simply a case of plugging in the second monitors then right click the desktop / properties/settings/ then follow the instructions (just one or two clicks)
So tell us more cos it could be a little more complex if you don't have the nessecary hardware or an antiquated OS.
It will work if you have onboard graphics and a separate graphics card in a slot and a monitor in bo the ports it will also work if you have a graphics card that supports two monitor or having two graphics cards in slots. As above then just right click desktop\Properties\Settings\advanced check the settings under one of the tabs