The Gallery block can be used to create a slideshow, allowing the visitor to easily move through a set of enlarged images.

Simple Gallery, Default Settings

The Gallery block is used to show a set of image thumbnails. By default, the thumbnails are displayed, in the chosen layout – based on the gallery sidebar settings – with no click-through effect.

Gallery Click-through Options

To allow site visitors to see a larger version of each gallery image, you can set the link behaviour for the gallery items.

Edit the Gallery block. (Use the breadcrumbs at the bottom of the page to be sure that you are editing the gallery block itself and not one of the individual images).

In the Block Controls toolbar (above the block), click on the link icon. This allows you to choose what happens when a site visitor clicks on one of the gallery images. You can choose to link to the full size image/media file, or to a lightboxed enlargement (the option to link to the attachment page is not usually useful).

Gallery with Link to Full Size Media File

The gallery below demonstrates the “Link images to media files” option. You can also choose “Open images in a new tab“, in the sidebar settings, which allows the visitor to stay on the original page while opening and viewing the larger images.

Gallery with Lightbox Effect

The gallery below demonstrates the “Enlarge on click” lightbox option, displaying the enlarged images with a lightbox effect.

Gallery Slideshow

A gallery with the “Enlarge on click” lightbox effect behaves as a simple slideshow by default, by enabling visitors to click on arrows at the sides to traverse through the images, or to swipe through on mobile.

For a more sophisticated slideshow effect, with interesting transitions, or including content other than images, a slider plugin, such as Smart Slider 3, or Carousel Slider Block, is needed.

But this simple “traverse to the next image” effect is a very good addition to make viewing a gallery a more user-friendly experience.

More About Images

Note that you can override the gallery settings, including the chosen link effect, for individual images, by choosing the link option (or other setting) at the level of the particular image.

This might be useful, for example to use a gallery of images to link to different web pages, rather than to enlargements. But when setting up a gallery for a slideshow, or to click through to enlargements, being able to set the link option at the gallery level makes it a very quick and easy process.

For more detail about images and the block editor, see 
Block Editor – Images 
Block Editor – Image Block
Block Editor – Cover Images

Also useful is Finding Your Way Around the Block Editor.