here I'm trying to add custom featured image to multiple images by default WP featured image but only one image we have to add. I want to add custom featured image with Multiple images for categories.i new to WordPress can anyone suggest me how to add these.
By definition that feature is only for one image, and if you need multiple featured images. you will need to design a new feature yourself.
It should be trivial (at least in the sense that there are many examples how to do it) to create a meta box which allow you to select a "gallery" instead one image, but you will need to add your wrapper APIs around that or come up with some scheme on how to use the featured image related API for that (I doubt there is a good way to do it, but maybe I am wrong).