Hi Andy,
Dropdown menus depend on the template - best to use JA_Purity (log in to backend yoursite/administrator) Select Extensions then Template Manager - click on the radio button for JA_Purity then top right click default.
Next go to Extensions/Modle Manager - we need to put a menu in the spot JA_Purity will show you drop downs.
Find the module Main Menu - open it and on the right you'll see a drop down menu Position - select 'hornav' next top right click save.
Look at you site now at the front end and the menu item Joomla! Overview will have one drop down item.
If you want to see how this is done go the your backend select Menus/Main Menu and you can see the structure.
Hope this helps
Ian
PS this assumes you have install the default data into your Joomla site
