Its uses are to generate more 0's and 1's that in turn represent different colored pixels to be output to your display of choice.
Here is a hint for you though, it sais ATI Radeon, so its not a 6/7000 series, so it's at least 2 years old. If you could name the ports on the back of the card, or upload a picture of it somewhere then we would have something better to go off of. If all else fails, try using google images to find a match.