So let’s get this straight, you want to make an animation that makes it look like a little square is following the line across this image (like a spark perhaps?) Something like this?…
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http://www.pbase.com/image/32799716>
To make animations in PSE you need to have each stage of movement (or frame) a separate layer. Then you would Save for Web, saving as a GIF checking the animate box. See page 219 of the PSE manual for details.
You really don’t need a lot of frames/layers to create the illusion of movement (the more layers you have the bigger the file size). It’s a little fussy because you have to have the background in each frame, but when you are creating the squares you need to keep them on a transparent layer to make it easy to duplicate for the next frame. If you need more details let me know.
If you like, download and save the gif I made above and then open it in PSE. You will be able to see the layers.
Patti