Can someone please give me the basic guidlines on how to build a Lightbox portfolio page using the "Portfolio Item Type" under "Parameters and Options" in Kalium?

I have managed to build "Side" portfolio pages successfully sing the "Portfolio Item Type" but I just cannot build a Lightbox portfolio page.

I add multiple images to the lightbox option but then the preview is simply blank! The only way I can get the lightbox to show is to add a "Featured Image" but then the featured image fills up the page completely and any other items on the page (texts etc.) dont show!

The lighbox option says: "Select what content type to show in Lightbox when user clicks on thumbnail." without any option or instructions about adding thumbnails etc.

I guess I am missing a very basic step (I am a novice) so I would be gratefull for any help. Unfortunately the Kalium support documents are very limited and they only basically explain the options and do not give the full procedures etc.

Many thanks.