Create sample page on the admin dashboard

create-page-wp-admin-dashboard.php

<?php
add_action( 'admin_menu', 'my_admin_menu' );
function my_admin_menu() {
  add_menu_page(
    __( 'My page name', 'my-textdomain' ),
    __( 'My menu name', 'my-textdomain' ),
    'manage_options',
    'sample-page',
    'my_admin_page_contents',
    'dashicons-schedule',
    3
  );
}
function my_admin_page_content() { ?>
  <div class="wrap">
    <h1>My Settings page</h1>
  // Notice sample
    <div id="setting-error-settings_updated" class="notice notice-success settings-error is-dismissible"> 
        <p><strong>Form updated.</strong></p><button type="button" class="notice-dismiss"><span class="screen-reader-text">Dismiss this notice.</span></button>
    </div>
  // Form
    <form name="form" action="" method="post">
        <input type="text" name="sample_field" value="">
        <p class="submit"><input type="submit" name="submit" id="submit" class="button button-primary" value="Save"></p>
    </form>
</div>
<?php
}