Okey, so you want to display thumbnails from the “featured image” field in the post editor, in a list on a page/post, but only want to display the thumbnails from a specific category? Well, where it is.
numberposts=6 is the number of thumbnails to show.
cat=3 is the ID of the category. (you can exclude categoryies too, just put a – in front of the ID. Like “cat=-3”)
This needs to be in one loop.