drupal/core/modules/help/help.module

<?php

/**
 * @file
 * Manages displaying online help.
 */

/**
 * Implements hook_menu().
 */
function help_menu() {
  $items['admin/help'] = array(
    'title' => 'Help',
    'description' => 'Reference for usage, configuration, and modules.',
    'route_name' => 'help.main',
    'weight' => 9,
  );

  $items['admin/help/%'] = array(
    'route_name' => 'help.page',
    'type' => MENU_VISIBLE_IN_BREADCRUMB,
  );

  return $items;
}

/**
 * Implements hook_help().
 */
function help_help($path, $arg) {
  switch ($path) {
    case 'admin/help':
      $output = '<h2>' . t('Getting Started') . '</h2>';
      $output .= '<p>' . t('Follow these steps to set up and start using your website:') . '</p>';
      $output .= '<ol>';
      $output .= '<li>' . t('<strong>Configure your website</strong> Once logged in, visit the <a href="!admin">Administration page</a>, where you may <a href="!config">customize and configure</a> all aspects of your website.', array('!admin' => \Drupal::url('system.admin'), '!config' => \Drupal::url('system.admin_config'))) . '</li>';
      $output .= '<li>' . t('<strong>Enable additional functionality</strong> Next, visit the <a href="!modules">Extend page</a> and enable modules that suit your specific needs. You can find additional modules at the <a href="!download_modules">Drupal.org modules page</a>.', array('!modules' => \Drupal::url('system.modules_list'), '!download_modules' => 'https://drupal.org/project/modules')) . '</li>';
      $output .= '<li>' . t('<strong>Customize your website design</strong> To change the "look and feel" of your website, visit the <a href="!themes">Appearance page</a>. You may choose from one of the included themes or download additional themes from the <a href="!download_themes">Drupal.org themes page</a>.', array('!themes' => \Drupal::url('system.themes_page'), '!download_themes' => 'https://drupal.org/project/themes')) . '</li>';
      // Display a link to the create content page if Node module is enabled.
      if (\Drupal::moduleHandler()->moduleExists('node')) {
        $output .= '<li>' . t('<strong>Start posting content</strong> Finally, you may <a href="!content">add new content</a> to your website.', array('!content' => \Drupal::url('node.add_page'))) . '</li>';
      }
      $output .= '</ol>';
      $output .= '<p>' . t('For more information, refer to the subjects listed in the Help Topics section or to the <a href="!docs">online documentation</a> and <a href="!support">support</a> pages at <a href="!drupal">drupal.org</a>.', array('!docs' => 'https://drupal.org/documentation', '!support' => 'https://drupal.org/support', '!drupal' => 'https://drupal.org')) . '</p>';
      return $output;
    case 'admin/help#help':
      $output = '';
      $output .= '<h3>' . t('About') . '</h3>';
      $output .= '<p>' . t('The Help module provides <a href="!help-page">Help reference pages</a> and context-sensitive advice to guide you through the use and configuration of modules. It is a starting point for <a href="!handbook">Drupal.org online documentation</a> pages that contain more extensive and up-to-date information, are annotated with user-contributed comments, and serve as the definitive reference point for all Drupal documentation. For more information, see the <a href="!help">online documentation for the Help module</a>.', array('!help' => 'https://drupal.org/documentation/modules/help/', '!handbook' => 'https://drupal.org/documentation', '!help-page' => \Drupal::url('help.main'))) . '</p>';
      $output .= '<h3>' . t('Uses') . '</h3>';
      $output .= '<dl>';
      $output .= '<dt>' . t('Providing a help reference') . '</dt>';
      $output .= '<dd>' . t('The Help module displays explanations for using each module listed on the main <a href="!help">Help reference page</a>.', array('!help' => \Drupal::url('help.main'))) . '</dd>';
      $output .= '<dt>' . t('Providing context-sensitive help') . '</dt>';
      $output .= '<dd>' . t('The Help module displays context-sensitive advice and explanations on various pages.') . '</dd>';
      $output .= '</dl>';
      return $output;
  }
}

/**
 * Implements hook_preprocess_HOOK() for block templates.
 */
function help_preprocess_block(&$variables) {
  if ($variables['plugin_id'] == 'system_help_block') {
    $variables['attributes']['role'] = 'complementary';
  }
}