This means that your website visitors will see the menu elements you categorised.
To create a submenu:
1.) Click on "Menu" => "Create submenu".
2.) At "Menu" => "Manage menu elements", you can move the menu items into a submenu by clicking on the arrows to the right of the menu item.
This means ONLY YOU can see folders, they are not publicly visible on your website (in contrast to submenus). Folders are useful to categorise your pages into different topics.
To create a folder:
1.) Click on "Pages" => "Create folder".
Manage folders: To delete a folder, change the title of a folder or edit the pages in the folder, click the appropriate location of the folder symbol.
2.) At "Pages" => "Manage pages" you can move the pages into your newly created folder by clicking on the arrows on the right of the page.