Juicebox stand alone is great and simple. But in Wordpress 4.9.8, I have spent hours and cannot work how to make a gallery.

I can make anative wordpress gallery:
[juicebox gallery_id="5"]

But I have read and re-read and cannot work out how to add images to the gallery. I have one photo added. I cannot work out how to manage the gallery and add or remove.

I tried to follow instruction on the websiite https://www.juicebox.net/support/wp-juicebox/
but I cannot get them to work.

HELP PLEASE!