The Galleries are viewable by two methods.  The default gallery structure shows a contact sheet of thumbnails which can be clicked to enlarge the image.  Once enlarged, manually click the forward or backward arrows at the bottom of each image to move through the gallery at your own pace.  Clicking anywhere within an image closes the viewer and returns to the thumbnail contact sheet.  If you prefer an automated slide show click on the [show as slide show] text at the top of the gallery and the slide show begins (four seconds per slide).