What you're trying do is entirely up to the theme you're using. Where you may need some code from here, is the CSS classes you can add to the multiple levels of menu. Using the base theme for your site, work out what the CSS classes need to be for your menus to hover and you will be able to get these to work.
Bootstrap 3 doesn't have hoverable menus. You can find several different answers on how to make them open on hover by googling. Good luck!