Ok, in this scenario imagine you are playing a video game. In the game, you are driving a car in the rain at a very high rate of speed. The car goes faster and faster until you hit a tree with the car and your character flies through the windshield and you lose a life or points or suffer some sort of consequence. The CPU is the brain that takes the math about your cars weight and speed and velocity and figures out how far your character will fly out the windshield and how much damage your character receives. Your GPU however will take the info processed by the CPU and turn it into an image that is able to be displayed on your monitor. ie: how your character's hair or clothes look in the rain or how light glances off the shiny metal of the car or metal.