<!DOCTYPE html>
<html lang="en">
<head>
<title>Bootstrap Example</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://apps.bdimg.com/libs/bootstrap/3.3.0/css/bootstrap.min.css">
<script src="https://libs.baidu.com/jquery/2.1.4/jquery.min.js"></script>
<script src="https://apps.bdimg.com/libs/bootstrap/3.3.0/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
<h2>Help text</h2>
<p>Use the .help-block class to add a block level help text in forms:</p>
<form>
<div class="form-group">
<label for="pwd">Password:</label>
<input type="password" class="form-control" id="pwd" placeholder="Enter password">
<span class="help-block">This is some help text that breaks onto a new line and may extend more than one line.</span>
</div>
<button type="submit" class="btn btn-default">Submit</button>
</form>
</div>
</body>
</html>