editing menu for dropdown as apposed to link

In a menu I want to know how to have a parent item (I don't mean parent in terms of URL, just menu) when clicked on, instead of linking to page, can expand the submenu it has under it. I can't post my URL, but this really is not theme or plugin specific anyway. I just want to know how a menu item can be used to open a submenu when clicked on, as opposed to linking to a page. Thanks so much for all your help and good luck with the new hosting thing!