ThumbnailsHere you decide on height width on the slide show thumbnails. There is always a thumbnail shown of the first image in the folder.
If you would like to sort manually in the image folder (right click on the folder and choose Sorting -> manual), you can then move images in the order you would like them by holding down shift and do a drag and drop.
Width paddingIf there should be a width between the thumbnails you set it here.
Height paddingHere you set the height between miniatures.