Help with Gallery format

I’m not sure what I’m doing wrong, but I can’t get the gallery format to work properly.

I tried adding a gallery bloc or individual pictures both times selecting the gallery format as post format, but it won’t do a slideshow like in the demo. All I see is the title & text of the post.

Do I need to have a specific plug in installed?

The page I need help with: [log in to see the link]