Page Layout – Link Buttons & Loading Content

I’ve been able to create pages that load posts for specific categories.

Now I want to create 3 buttons on the top of a page with each button linking to a specific page.

Ideally, I’d want the contents of the pages to load underneath the 3 buttons and on the same page. Sort of like a page within a page.

I’m stumped! How can I go about creating this?

Any help would be greatly appreciated!