There is a lot of information here, probably too much for those truly unfamiliar with programming.
Raster graphics describe an image as an array of colored pixels.
A 512x512 raster image displays with a size of about 7 inches by 7 inches on a typical monitor. Vector graphics describe an image independent of the resolution of the final rendering device. When this is plotted on a 600 dpi printer it will look much smoother than the same graphic rendered on a monitor. Raster graphics are the only reasonable choice for photos and satellite images. Raster graphics cannot be converted back to vector graphics.