Changing Pages to Categories

Hello,

I love this theme and want to keep using it so really hoping someone can help me. I’d like to convert the pages that run along the top menu bar to categories. That way, when I’m writing a blog post, whatever corresponding category I select will automatically populate that page in addition to the home blogging page.

So, for example, if I’m writing a book post, selecting a ‘book’ category will automatically fill the book page.

Any help much appreciated! Thanks!