(1) In computer graphics, to "paint" the screen means using a stylus on a digitizer tablet or a mouse to simulate a paintbrush. See
paint program.
(2) To transfer an image as in the phrase "the laser printer paints the image onto a photosensitive drum."
(3) To create a screen form by typing anywhere on screen. To "paint" the screen with text.
(4) For Microsoft's program, see
Microsoft Paint.