You have to have a graphics card which has two outputs compatible with both monitors. Just take a look at the connectors on the monitors. To see If you have DVI or VGA
Then look behind your computer to see if you have two outputs that match up. If so, great! you can configure the settings by right clicking on the desktop and going to the graphics card configuration window. If your graphics card doesn't have the supported output you would need a new one before you could have dual monitors.
if your card doesn't have to outputs, you can usually get a cheap old pci graphics card, connect it, and connect a second monitor to it. I'm not sure if it will show your games properly though, so it depends on what you're using it for. It may display your games properly, I'm not sure.