How to connect category specified post in a page!

Site: https://www.oliverjordan.com

As I read many times in the last day, there are so many people wondering how to connect a post under a specific category to show on a specific page. I have tried numerous times to find a plugin and I have installed “Category Pages & Posts” plugin, but I don’t know where to add the “showauto” of “shortcode.” I’m not to the knowledgable as to css coding. Is there anyone that can help me do this in the most clear way possible? It would be so greatly appreciated!