How to make multiple admin pages for one plugin?

Using add_submenu_page function WordPress you can add multiple pages/menu

In order to add a new top-level menu to WordPress administration dashboard, You can use add_menu_page() function. This function has the following syntax.

//add plugin menu

     add_menu_page($page_title, $menu_title, $capability, $menu_slug, $function, $icon_url, $position);

As you can see, The function accepts the following parameters.

page_title: The page title.

menu_title: The menu title displayed on the dashboard.

capability: the Minimum capability to view the menu.

menu_slug: Unique name used as a slug for the menu item.

function: A callback function used to display page content.

icon_url: URL to a custom image used as the icon.

position: Location in the menu order.

Adding a Submenu

There are two types of submenus, menu items listed below your top-level menu and menu item listed below existing default menus in WordPress. To add submenus under your top-level menu, You can use add_submenu_page() function. This function has the following syntax.

//add submenu
add_submenu_page($parent_slug, $page_title, $menu_title, $capability, $menu_slug, $function);

As you can see, this function accepts the following parameters.

parent_slug: Slug of the parent menu item.

page_title: The page title.

menu_title: The submenu title displayed on the dashboard.

capability: the Minimum capability to view the submenu.

menu_slug: Unique name used as a slug for submenu item.

function: A callback function used to display page content.

Ex:

add_action('admin_menu', 'my_menu_pages');
function my_menu_pages(){
    add_menu_page('My Page Title', 'My Menu Title', 'manage_options', 'my-menu', 'my_menu_output' );
    add_submenu_page('my-menu', 'Submenu Page Title', 'Whatever You Want', 'manage_options', 'my-menu' );
    add_submenu_page('my-menu', 'Submenu Page Title2', 'Whatever You Want2', 'manage_options', 'my-menu2' );
}