want to show a menu in this admin panel
You need to use add_menu_page and add_submenu_page to display menu and sub menu.
This can be done in a few ways.
It's probably best if you familiarise yourself with the WordPress Settings API and then look at the WordPress documentation on Creating Options Pages
WordPress Settings API: https://codex.wordpress.org/Settings_API
Creating WordPress Options Pages: https://codex.wordpress.org/Creating_Options_Pages
Another way of creating theme options pages quickly is to use a plugin such as the Redux Framework: https://en-gb.wordpress.org/plugins/redux-framework/