Usually while trying to setup menu in joomla, beginners get confused how to show sub menu items in the menu (in top menu for example).
These settings are found in the menu module settings.
To enable showing sub menu items in Joomla follow these steps:
1. Login to Joomla! admin panel
2. goto: Extensions > Module Manager
3. Select your menu module and edit it
4. On the right hand side, under “Basic Options” select “Yes” for “Show sub-menu items”
5. Save
This will now enable submenu items to be shown on your joomla menu.