Under the tab Appearance on the dashboard should be the tab "Menu" where you can make a custom menu and develop a hierarchy in the menu resulting in dropdown pages.
Create a custom menu, by selecting create menu, give it a name, and add it as the primary menu. Add the pages that you want referenced into the menu. You can then drag a page onto an existing page in the create a menu space. This will allow it to become part of that "main page" and be visible as a drop down menu. You can create menu item to reference a category or a tag type and add them to an item as well. Hope this helps a little as I am not a WP expert so explaining it is not what I am good at.