An image gallery is a special type of image slideshow. Galleries have navigation controls that allow your visitors to scroll through images at their own pace. You can add captions to each image in a gallery to tell your visitors a story.
To enable image gallery functionality, select the Show Gallery Controls option for your image slideshow.
To add a caption to an image, click the speech bubble icon in the left corner of the image thumbnail.
Please see Create an Image Slideshow for details about adding, removing, and reorganizing images.