Untitled

<!doctype html>
<html>
<head>
 <meta http-equiv="X-UA-Compatible" content="IE=edge" >
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <script src="js/lib/jquery/jquery-1.10.2.js"></script>
    <script src="js/lib/bootstrap/js/bootstrap.js"></script>
    <link rel="stylesheet" href="js/lib/bootstrap/css/bootstrap.min.css" media="screen"/>
</head>
<body>

<div class="container">
<div class="row">
        <div class="col-md-5">
            <button type="button" class="btn btn-default btn-lg">
               <span class="glyphicon glyphicon-arrow-left"></span>Back
             </button>
        </div>
</div>
</div>
</body>
</html>

<span class="glyphicon glyphicon-arrow-left"></span>

<body>
       <button type="button" class="btn btn-default btn-lg">
       <span class="glyphicon glyphicon-arrow-left"></span>Back</button>
</body>