Choosing a graphics card can be overwhelming if you have not put time and effort into researching what you want, what you need, and what is available on the market. For more information about what a graphics card is, why you need one, and why you would want to upgrade your existing one, please see Computer Components: Video Card.
Obviously, it is important to have a decent graphics card, because everything your computer displays has to be processed by the graphics card. If you are using your computer for standard email and word processing tasks, it is not really important to have a great card. If you use your computer to play games, or you use your computer to design graphics and web sites, you probably need one of the higher end cards.