You will need a dedicated GPU that has two outputs (basically all of them do).
If you could post information on your computer, intended usage and a budget, we could help get you pointed in the right direction.
There are two ways to be sure.
You could either open the case and visibly check or you could post the brand and model of your system and I can check the net.
Assuming it is a fairly recent computer (built in the last 4 or 5 years) it most likely does have a free PCIe slot.
Well, that is a quite Old Motherboard.
There are no PCIe slots but there is an AGP slot.
For $33 you could get a new* AGP GPU with dual display outputs (*the card is new but the chip used is of quite old design, do not expect to be able to game on it).