Dual Monitor?

Okay, please ignore my supreme ‘n00byness’ on hardware stuff. I’m not a wizard.

Question: What is needed to run two monitors?

My graphics card is a ‘256MB NVidia GeForce 8300 GS’ (not best and I will probably upgrade after Christmas).

I think I only have one monitor port/plug thingy on back of my machine so is there just some sort of adapter I could get?

OS: Vista