Along the left edge, under the Galleries heading is the list of available photo galleries. Click on one of them to display that gallery in the main window area.
Place your cursor over one of the small thumbnail images and it will grow slightly larger. If you then click on the thumbnail, it will be show in the large image area.
The PLAY control will start an automatic slide show, starting with the currently showing image. Each image will be shown for about 6 seconds. Click the PAUSE button to stop the slide show.
The NEXT control will stop the slide show (if going) and display the next image, while PREVIOUS will show the previous photo in the gallery.