I don't see the description

Yes it does.
But not in all views.
You can add desctiption in Content Popup, Content Slider, Slider, views

hmm, having description up in lightbox view is probably the feature that everyone wants, I opened lightbox.css and looking at #imagedata.

Is there a way to add description to it ?

Dear user it is not impossible to add description in Lightbox,
because Lightbox is image, so we can not make a space for description in image.
I recommend you to pay attention to our Content Popup View

Thank you