Go away, do not sign up to this forum where we actually try to help people who need help not people asking stupid questions, If you really dont know what one is then google it, its much easier than signing up to here
The Graphics card is responsible for delivering the image you see on your PC monitor. Its GPU (Graphics Processing Unit) processes the data and changes it into a signal to the monitor. There are many factors to a graphics card. Choosing one can be a tricky business these days as there is so much technology that is different in each new graphics card release. More of these later in the article.
So what are you really wanting to know? Let me ask you a question? Tell me what you think a graphics card is? Then that way we will be able to fill in the holes and make your understanding more sophisticated about the GPU.