Hi Jane,
You can create pages with sub-pages in the Content Management System and, as long as you turn on Include in navigation menu for those pages then they'll appear approprately in the menu structure.
If you select a nav bar style in the Bootstrap theme then these will appear as popup menus under the main menu item.
This is how the sub-menus are done on the Voice demo site - this is currently using the Modern theme, but the menus will be similar in the Bootstrap theme.
The Site Map in the CMS looks like this for the Demo Site:
You can't place applications such as the Calendar or Photo Album in sub-menus - these have to be at the top level of the site. Though one "trick" you can do is to enable the application but turn off Show in Navigation, then create a Redirect page in a sub-menu in the CMS that redirects to the application.
Hope that helps!
Joe - Voice Admin