line calls the pygame display update(functionwhich draws the surface object returned by pygame display set_mode(to the screen (remember we stored this object in the displaysurf variablesince the surface object hasn' changed (for exampleby some of the drawing functions that are explained later in this the same black image is redrawn to the screen each time pygame display update(is called that is the entire program after line is donethe infinite while loop starts again from the beginning this program does nothing besides make black window appear on the screenconstantly check for quit eventand then redraws the unchanged black window to the screen over and over again let' learn how to make interesting things appear on this window instead of just blackness by learning about pixelssurface objectscolor objectsrect objectsand the pygame drawing functions pixel coordinates the window that the --hello world|program creates is just composed of little square dots on your screen called pixels each pixel starts off as black but can be set to different color imagine that instead of surface object that is pixels wide and pixels tallwe just had surface object that was pixels by pixels if that tiny surface was enlarged so that each pixel looks like square in gridand we added numbers for the and axisthen good representation of it could look something like thiswe can refer to specific pixel by using cartesian coordinate system each column of the xaxis and each row of the -axis will have an --address|that is an integer from to so that we can locate any pixel by specifying the and axis integers for examplein the above imagewe can see that the pixels at the xy coordinates ( )( )( )and ( have been painted blackthe pixel at ( has been painted graywhile all the other pixels are painted white xy coordinates are also called points if you've taken math class and learned about cartesian coordinatesyou might notice that the -axis starts at at the top and then increases going downrather than increasing as it goes up this is just how cartesian coordinates work in pygame (and almost every programming language