Issue #2999731 by tim.plunkett, r.aubin, bnjmnm, tedbow: Document Layout...

Issue #2999731 by tim.plunkett, r.aubin, bnjmnm, tedbow: Document Layout Builder functionality in its hook_help() text

core/modules/layout_builder/layout_builder.module

@@ -47,8 +47,15 @@ function layout_builder_help($route_name, RouteMatchInterface $route_match) {
   switch ($route_name) {
     case 'help.page.layout_builder':
       $output = '<h3>' . t('About') . '</h3>';
-      $output .= '<p>' . t('Layout Builder provides layout building utility.') . '</p>';
-      $output .= '<p>' . t('For more information, see the <a href=":layout-builder-documentation">online documentation for the Layout Builder module</a>.', [':layout-builder-documentation' => 'https://www.drupal.org/docs/8/core/modules/layout_builder']) . '</p>';
+      $output .= '<p>' . t('Layout Builder allows you to use layouts to customize how content, custom blocks, and other <a href=":field_help" title="Field module help, with background on content entities">content entities</a> are displayed.', [':field_help' => Url::fromRoute('help.page', ['name' => 'field'])->toString()]) . '</p>';
+      $output .= '<p>' . t('For more information, see the <a href=":layout-builder-documentation">online documentation for the Layout Builder module</a>.', [':layout-builder-documentation' => 'https://www.drupal.org/docs/8/core/modules/layout-builder']) . '</p>';
+      $output .= '<h3>' . t('Uses') . '</h3>';
+      $output .= '<dl>';
+      $output .= '<dt>' . t('Default layouts') . '</dt>';
+      $output .= '<dd>' . t('Layout Builder can be selectively enabled on the "Manage Display" page in the <a href=":field_ui">Field UI</a>. This allows you to control the output of each type of display individually. For example, a "Basic page" might have view modes such as Full and Teaser, with each view mode having different layouts selected.', [':field_ui' => Url::fromRoute('help.page', ['name' => 'field_ui'])->toString()]) . '</dd>';
+      $output .= '<dt>' . t('Overridden layouts') . '</dt>';
+      $output .= '<dd>' . t('If enabled, each individual content item can have a custom layout. Once the layout for an individual content item is overridden, changes to the Default layout will no longer affect it. Overridden layouts may be reverted to return to matching and being synchronized to their Default layout.') . '</dd>';
+      $output .= '</dl>';
       return $output;
   }
 }