Category and Post display

Hello, This is my first post here and i’m no programmer, so forgive my ignorance. I’ve searched for this all over and haven’t found anything that matches what i’m looking for so here goes:

I’m wanting to display all posts from a specific category as well as the respective subcategories on a page and have the names of the category and subcategories show up as well. I’ve created an example of what this should look like here: https://www.stefananion.com/dev/main-category

I’ve found a few plugins, that do part of the job, like showing all posts for a specific category, but none of them seem to let you customize it the way i’d like it. I’m somewhat familiar with how WP works, but i’m no expert by any means. I appreciate the help ??