Adding a tab to the WordPress Dashboard

This code snippet add a tab to the WordPress Dashboard as seen below

add_action( 'admin_menu', 'myfirsttab' );

function myfirsttab(){
    add_menu_page( 'my_first_tab', 'My First Tab', 'administrator', 'my_first_tab', 'my_first_tab_code', 'dashicons-external', null ); 
}

function my_first_tab_code(){
    echo "<h3>My First Tab is here!</h3>";
}