It will contain an array of four images. Preload the images.
A timer will be set so that a new image replaces another image every 10 seconds.
If the user clicks a button labeled Start, the timer starts the image replacement.
If the user clicks a button labeled Stop, the timer stops it.
I changed the time to 3 seconds so you don't have to wait a long time to see it move.
I added PREVIOUS and NEXT buttons. These do what they say and they also stop the slideshow timer.