Category pages question

I have created my pages and the category pages that I want attached to each page. I have added these to the custom menu and created my navigation for the website. Say I have a page link on my navigation that says “music” and a category page drops down called “chill.” When I post a new post and have it set to the category “chill” I can see it there. How can I click on the “Music” tab and have it show all the content within the category pages linked to it.

Example tab:
Music
-chill
-dub
-electronic

Say I have category pages: chill, dub, and electronic. I am able to post to those category pages. These category pages are all dropping down off the Music menu. How can I click on “Music” and have it show the content within chill, dub, and electronic??