Image in modal doesn't work.

Hello Guys.
I have problem. I'd like to display images lightbox effect or something similar . When i use class modal do not show the picture.
I am a beginner, you can hint how can I nicely display images?

I installed the add-on nonumber modals and shows me a picture but does not create a gallery.

site : http://insertmedia.pl/domeknadpopradem
Thank you!