The "N" in this image? All animation is a repeated movement of the same image OR the fading in and out of the same image by changing the opacity of the image.
The "N" represents the number of times the chosen image will be duplicated, to understand how it works I suggest this. Take 1 image and set the "N" to 2 and set the first image ("N" point 1) to the left side of the screen and then the second image ("N" point 2) to the right side of the screen. Play it, the image will jump from the left to the right.
Then go back and set "N" to 5 and move the images (various points) to different places on the screen, play that and the image will appear to jump around.
The more "N" point images the easier it is to make an image appear to change just slightly, the less "N" point images the greater the change.
Hope that helps!