Here’s an easiest and fastest way of adding JQuery effect in your default WordPress menus in just a click. Menu Effect is a free WordPress plugin that lets you add JQuery effects on your default WordPress menus (including both drop down main and sub menu) without changing or editing any code.
All you need to do is install and activate Menu Effect plugin in your WordPress site and you are done. Everything else it does automatically, it gives you ” Slide Up ” and ” Slide Down ” JQuery effect but you must register your menu as primary using Appearance -> Menu and set your primary menu.