Wordpress create menu and submenu on admin side.

function admin_left_panel() {
    add_menu_page('Page Title', 'Left menu label', 'manage_options','pageurl1', 'menu_one');
    add_submenu_page('pageurl1', 'Page Title','Left menu label 2', 'manage_options', 'pageurl2','menu_two');
    add_submenu_page('pageurl1', 'Page Title','Left menu label 3','manage_options', 'pageurl3', 'menu_three');
}

add_action('admin_menu', 'admin_left_panel');

function menu_one() {
    echo '<div class="wrap"><div id="icon-options-general" class="icon32"><br></div><h2>Page 1</h2></div>';
}

function menu_two() {
    echo '<div class="wrap"><div id="icon-options-general" class="icon32"><br></div><h2>Page 2</h2></div>';
}

function menu_three() {
    echo '<div class="wrap"><div id="icon-options-general" class="icon32"><br></div><h2>Page 3</h2></div>';
}