Slide Shows: To view all the pictures in a Gallery as a Slide Show, point to any picture with the mouse and an option called "Slideshow" will appear. If you click the "Slideshow" option, a new window will open and all the pictures will be displayed, one at a time, for a few seconds each.
Picture Viewer: If you click on any picture in the Gallery, a new window will open for the picture viewer. This window will allow you to view the pictures in full size and manually (with the mouse) move to the next or previous picture in the Gallery.