display sub sub menu items under their parents

I’m trying to show the sub-submenus of my website under their parent menu node, much like the oracle website. I installed a theme named Oracle, which looks good. My requirement now is to show the sub sub menus directly under their parents (in columns if possible), and not while hovering on their parents. I just need some indications on where I could tweak the code for creating menus and sub menus, in order to change the resulting HTML and CSS.