Dropdown Bootstrap

gmana caranya bikin dropdown menu dengan bootstrap 3.3.6, sya udah cari2 refrensi di dokumentasi bootstrap tpi tetp ga berhasil.. mohon koreksinya gan,, baru belajar bootstrap..

	<nav class="navbar navbar-inverse">
	<button type="button" class="navbar-toggle btn btn-inverse" data-toggle="collapse" data-target="#menu" data-parent="#menu">
	<span class="icon-bar"></span>
	<span class="icon-bar"></span>
	<span class="icon-bar"></span>
	</button>
	<a href="index.php" class="navbar-brand">
	<span>Ngoding</span>
	</a>

	<div class="collapse navbar-collapse" id="menu">
	<ul class="nav navbar-nav">
	<li class="active"><a href="index.php">Beranda</a></li>
	<li><a href="download.php">Download</a></li>
	<li><a href="#" type="button" class="dropdown open dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="true">Kategori <span class="caret"></span></a>
	<ul class="dropdown-menu">
	<li  class="dropdown-item"><a href="#"></a>Teknologi</li>
	<li  class="dropdown-item"><a href="#"></a>Olahraga</li>
	</ul>
	</li>
	</ul>

	<form action="" method="GET" class="navbar-form navbar-right" role="search">
	<div class="form-group">
	<input type="search" name="cari" class="form-control search-query" placeholder="Cari disini...">
	</div>
	</form>
	</div>
</nav>