Galleries come with a set of stock images to show you an example of each gallery's layout. At anytime, you can add your own images to the gallery.
Here's how:
On the website page, click the gallery.
The settings panel opens on the right side of the Website Builder.
Click the icon to open the Image Order settings.
Click the Click here to add images button.
The Content Manager opens.
In Stock or My Images, drag images from the Content Manager to the Drag images here to add to your gallery area.
The image now appears in the gallery.
Click the icon to close the settings.
The images appear in the gallery.