Click on the plus sign to the right of Related Objects and choose Add Gallery.
Give your Gallery a name and a description.
Choose Save when you are done.
Add images in the Media Management section that will populate your Gallery.
You can click the pencil to the right of each image to add a caption.
Save and Exit when you are finished editing.
Setting the Default Image
In the Media Management panel, you can upload one image that will be the default image of your slideshow. Make sure to mark this image as default. The default image will appear at the top of the page as a gallery. You will see the camera icon at the top that denotes this feature. It will use all the images you previously defined as a gallery within the feature.