This is a simple way in which you can present a 'slideshow' of pictures about a page. ANY page type (weekly meeting, event, 'general page', Charter Celebration) can have a 'slideshow'.
If you enter pictures into the slideshow for a page, it is automatically displayed in the 'Photo Galleries' page, linked from the horizontal menu. When the page opens, the 'slideshow' is automatically active, i.e. the pictures are displayed one after another.