Create Submenus / Drop Downs for Header Menus on Website

I have a simple site with 7 header menus. I would like to have the code added to the site to allow me to create additional pages and have them appear in drop down submenus under these header menus. I just need the code added and the instructions to add new pages with HTML to appear in these drop downs. The site is hosted with hostgator so it should be easy with Cpanel access to add the code / CSS or whatever it needs. Thanks in advance for your interest!