WIth most laptops you will have either a VGA out or a DVI out on either the side or back of the laptop. A VGA port is blue in color and looks like this
http://www.traderock.com/images/Img624.jpg
A DVI is usually but not necisarily white and looks like this
http://www.ngohq.com/images/articles/7800gtx/Pictures/Dual%20DVI.JPG
You also could have a mini DVI port which looks much like the DVI port but is about half the size.
Once you make sure that your laptop has one of these (which almost any laptop in the past few years has one) Go get yourself a monitor that preferribly has the same port that your laptop has. There are adapters available if your monitor does not match your laptop. Once your monitor is connected right click on the desktop and choose properties. Then choose to use the secondary monitor. (Sorry I cant remember what tab to choose as i am using a mac now and cant look at the moment it is the last tab though i remember that)
Hope this helps.
