To add a drop down menu, create a menu item that either links to a single article or a list of articles.

Once you create the menu, simply click on the heading under which the menu item needs to drop down. E.g. in our example, you see that the link "Community Central" appears as a drop down underneath "Community". This is done by highlighting "Community" in the parent item box. This tells the system that "Community Central" needs to drop down underneath "Community":