This page is using the Slideshow page template. To create a slideshow using the Slideshow page template, you’ll first need to create and publish a page withe the “Slideshow” page template applied to it.
If using the classic editor: Within the page editor, add a gallery by selecting Add Media > Create Gallery. Select your images, then click the blue “Create A New Gallery” button.
If using the Gutenberg editor: You will need to add the slideshow gallery by using the Shortcodes block, and listing the image ID numbers within the shortcode. You can find the image number by selecting “Media” in the dashboard, then clicking on an image. The number displayed at the end of the URL at the top is the image number. The following Codex page explains the Gallery Shortcode in greater detail: https://codex.wordpress.org/Gallery_Shortcode. It should look like this:
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