Это html:
<!DOCTYPE HTML>
<html>
<head>
   <meta charset="UTF-8"/>
<link  href="menushechka.css" type="text/css"  rel="stylesheet" />
<script type="text/javascript" src="node_modules/jquery/dist/jquery.min.js"></script>
<script type="text/javasript" src="menushechka.js" ></script>
    <title>Навигация</title>
</head>
<body>
    <nav>
      <ul id="ddmenu">
        <li><a href="#">Главная</a></li>
        <li><a href="#">О нас</a>
          <ul>
<li><a href="#">Миссия</a></li>
            <li><a href="#">Команда</a></li>
            <li><a href="#">История</a></li>
          </ul>
        </li>
        <li><a href="#">Продукты</a>
          <ul>
            <li><a href="#">Логитипы</a></li>
            <li><a href="#">Шаблоны</a></li>
           <li><a href="#">Иконки</a></li>
<li><a href="#">Плагины jQuery</a></li>
            <li><a href="#">маркетинг Internet</a></li>
          </ul>
        </li>
        <li><a href="#">Интернационализация</a>
          <ul>
            <li><a href="#">Китай</a></li>
            <li><a href="#">Япония</a></li>
            <li><a href="#">Канада</a></li>
            <li><a href="#">Автсралия</a></li>
            <li><a href="#">Южная Америка</a></li>
 </ul>
        </li>
        <li><a href="#">Контакты</a></li>
      </ul>
    </nav>
</body>
</html>
 
 Мой css:
html, body, div, span, applet, object, iframe, h1, h2, h3, h4, h5, h6, p, blockquote, pre, a, abbr, acronym, address, big, cite, code, del, dfn, em, img, ins, kbd, q, s, samp, small, strike, strong, sub, sup, tt, var, b, u, i, center, dl, dt, dd, ol, ul, li, fieldset, form, label, legend, table, caption, tbody, tfoot, thead, tr, th, td, article, aside, canvas, details, embed, figure, figcaption, footer, header, hgroup, menu, nav, output, ruby, section, summary, time, mark, audio, video {
  margin: 0;
  padding: 0;
  border: 0;
  font-size: 100%;
  font: inherit;
  vertical-align: baseline;
  outline: none;
  -webkit-font-smoothing: antialiased;
  -webkit-text-size-adjust: 100%;
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
}
html { height: 101%; }
body { background: #eaeaea url('images/bg.png'); font-size: 62.5%; line-height: 1; font-family: Arial, Tahoma, sans-serif; padding-bottom: 60px; }
 
article, aside, details, figcaption, figure, footer, header, hgroup, menu, nav, section { display: block; }
ol, ul { list-style: none; }
 
blockquote, q { quotes: none; }
blockquote:before, blockquote:after, q:before, q:after { content: ''; content: none; }
strong { font-weight: bold; }
 
table { border-collapse: collapse; border-spacing: 0; }
img { border: 0; max-width: 100%; }
#ddmenu {
  display: block;
  width: 100%;
  height: 80px;
  margin: 0 auto;
  padding: 0 15px;
  background: #fff;
  border-radius: 6px;
  border: 1px solid rgba(0, 0, 0, 0.15);
  box-shadow: 0 1px 1px rgba(20, 20, 20, 0.2);
  cursor: pointer;
  outline: none;
  font-weight: bold;
  color: #8aa8bd;
}
 
#ddmenu li { display: block; position: relative; float: left; font-size: 1.45em; text-shadow: 1px 1px 0 #fff; border-right: 1px solid #dae0e5; }
 
#ddmenu li a {
  display: block;
  float: left;
  padding: 0 12px;
  line-height: 78px;
  font-weight: bold;
  text-decoration: none;
  color: #6c87c0;
  -webkit-transition: all 0.2s linear;
  -moz-transition: all 0.2s linear;
  -o-transition: all 0.2s linear;
  transitio: all 0.2s linear;
}
#ddmenu li:hover > a { color: #7180a0; background: #d9e2ee; }
 
#ddmenu ul {
  position: absolute;
  top: 88px;
  width: 130px;
  background: #fff;
  display: none;
  margin: 0;
  padding: 7px 0;
  list-style: none;
  border-radius: 3px;
  border: 1px solid rgba(0, 0, 0, 0.2);
  box-shadow: 0 0 5px rgba(0, 0, 0, 0.2);
}
#ddmenu ul:after {
  content: "";
  width: 0;
  height: 0;
  position: absolute;
  bottom: 100%;
  left: 8px;
  border-width: 0 8px 8px 8px;
  border-style: solid;
  border-color: #fff transparent;
}
 
#ddmenu ul:before {
  content: "";
  width: 0;
  height: 0;
  position: absolute;
  bottom: 100%;
  left: 4px;
  border-width: 0 10px 10px 10px;
  border-style: solid;
  border-color: rgba(0, 0, 0, 0.1) transparent; 
}
 
#ddmenu ul li {
  display: block;
  width: 100%;
  font-size: 0.9em;
  text-shadow: 1px 1px 0 #fff;
}
 
#ddmenu ul li a {
  display: block;
  width: 100%;
  padding: 6px 7px;
  line-height: 1.4em;
  -webkit-transition: all 0.2s linear;
  -moz-transition: all 0.2s linear;
  -o-transition: all 0.2s linear;
  transition: all 0.2s linear;
}
#ddmenu ul li a:hover {
  background: #e9edf3;
}
  
$(document).ready(function(){
  $('a').on('click', function(e){
    e.preventDefault();
  });
  $('#ddmenu li').hover(function () {
     clearTimeout($.data(this,'timer'));
     $('ul',this).stop(true,true).slideDown(200);
  }, function () {
    $.data(this,'timer', setTimeout($.proxy(function() {
      $('ul',this).stop(true,true).slideUp(200);
    }, this), 100));
  });
});
P.S.: путь до jQuery я указал, согласно официальному сайту. Цитирую:"This will install jQuery in the node_modules directory. Within node_modules/jquery/dist/ you will find an uncompressed release, a compressed release, and a map file." Указал тот , что compressed.