Create an Image Gallery
What is an Image Gallery?
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.
Enable Gallery Mode
To enable image gallery functionality, select the Show Gallery Controls option for your image slideshow.
Add image captions
To add a caption to an image, click the speech bubble icon 
in the left corner of the image thumbnail.
Add, remove, and organize images
Please see Create an Image Slideshow for details about adding, removing, and reorganizing images.