Creating pages that only display posts of specific categries

I would like to know how I can create pages that will only read/recognize/display blog posts of a certain category instead of displaying all posts of all categories at once.

Please observe the problem in action:

Go to https://buyblacknyc.com/
Hover over the “Growth” link near the top
Click the “self-development” tab
Then click the “business development” tab.

Notice there is no change between the two.

Both pages are displaying all posts of all categories.
I would like to know how to create pages that selectively display posts based on their category.

Currently, both pages are under the parent page “Growth”, structured by the [Growth] template.
Nothing (no code, text, etc) is in the main body. Parent and template are the only things I have touched from the back end.

Any advice would be appreciated !
Give Thanks