WordPress particular posts from category

Hello i have a little problem here now i use unique theme (https://demos.appthemes.com/clipper/) on WordPress that uses it’s own categories and I need create specific categories in that theme section in order to add products to those categories and normal posts that WordPress uses are used only for blog section and i know that there is a lot of plugins that gives ability to display specific posts from particular category and put that like widget in sidebar but i did not find single that gives option choose those categories that are in that particular theme section i mean those categories that i want display it simply wont spot those and why should they spot there is not default WordPress.

So my questions is there is any plugin/easy way to do what i want here without any bug development of unique widget? (Could be any way I’m open to all suggestion). Thank you!