Ignoreing all the terminology:
You only have one graphic output atm, with an anolog signal and a DB15 connector.
You want to connect multiple monitors.
There are two ways to do that:
- Add a graphics card with more outputs. For non gaming purposes a cheap (€80-ish) card with 2 or 3 outputs will do just fine, and you can use both these and the current DB15/VGA connector.
- Split the output from your current DB15/VGA over multiple screens.
The last will mean you have the same image on both screens. Might be useful in a classroom with one image on the screen and an other on a projector.
The first option seems much more sensible. Adding more graphics outputs can be done with PCI-e cards (simple, works at boot, usually provides moder outputs which means you can use a modern monitor). If atr all possible I would go for a second minitor with display port and a cheap card with a pair of display port outs.
Note that even one DP out can be used to chain to multiple monitors as long as all use DP 1.2 and MST.
A more portable solution is an USB based external card. This sounds great, but performace is much lower and the sole experience I have with that (one USB card on two laptops) is awful. Graphical artifacts, no screen updating if you rotate it 90 degrees, bloue screens, etc etc. That might be just bad luck with a USB32HDEH but it makes me reluctant to advice this route.