add new addministration menu

I also want to learn this. I’ll share what I found so far. I learned this from a book on WordPress plugin development.

The book indicated [that inside the WordPress plugin you’re writiting,] the add_menu_page() function is what does the actual work of Creating a Top-Level Menu, which will be added to the left-hand-side admin dashboard menu list.

so I googled this term:
wordpress add_menu_page(

And it brought me to:
the Function Reference/add menu page

which describes how to:
“…creates a new top level menu section in the admin menu sidebar and…”