There's an onboard graphics system built into most motherboards that will handle basic graphics for people who don't use software that requires high-end graphics capacity. If your primary computer use is e-mail, Word, and things like that, you can get by with this.

Also on the motherboard will be one or more slots for an additional graphics card. In many cases, the slots are specifically designed for them. You can buy graphics cards that are better than what the motherboard system can deliver, or for real fanatics, much better. I've seen gaming systems with two or more heavy-duty cards running together. These handle the massive requirements of real-time 3D manipulation and coloring without having to rely on the main processor. Most such cards have their own cooling fans.

Odds are the card in that slot isn't a graphics card. All graphics cards have their own ports that plug into the displays, some of them with several options.

If you can find out the motherboard part number or type, I can give you more useful information.