Well, if you made it to this site you probably have an above average understanding of how to setup multiple displays. For the sake of everyone else I will try to be as thorough as possible in this explanation.
We’ll start with trying to identify what different things everyone reading this might have. Most people start with one display and then for whatever reason decide that it would be cool to add a second display. Let us assume for one minute that you are one of these people. First things first. We need to do an equipment check.
What type of graphics card are you using? Most people have something like this:
This configuration shows VGA, SVIDEO, and DVI connectors. However, this is not the only configuration possible, there is also this possibility: