html

<?php
if (isset($_POST['submit'])) {
	$username = $_POST['username'];
	$password = $_POST['password'];
	$email = $_POST['email'];

	$conn = mysqli_connect('localhost', 'root', 'root', 'simple');
	$sql = "INSERT INTO user(username, email, password) VALUES('$username','$email' ,'$password');";
	if (mysqli_query($conn,$sql)) {
		echo "Data inserted!";
	}else {
		echo "Data insert failed".mysql_connect_error();
	}
      //   echo "Your name: ".$username."<br>";
	  // echo "Your email: ".$email."<br>";
	  //    echo "Your password: ".$password."<br>";

}

 ?>


<!DOCTYPE html>
<html>
<head>
	<title>PHP</title>
	<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">

</head>
<body>
	<h1 class="display-3 text-center">PHP excercise</h1>
	<hr>

	<div class="container">
		<div class="col-sm-4 col-12">
			<form method="POST">
				<p><input type="text" name="username" class="form-control" placeholder="Your username"></p>
				<p><input type="email" name="email" class="form-control" placeholder="Your email"></p>
				<p><input type="password" name="password" class="form-control" placeholder="Your password"></p>
				<p><button class="btn btn-success" type="submit" name="submit">Submit</button></p>
			</form>
		</div>
	</div>

	<div class="container">

	</div>
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/			rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
	<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script>
	<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js" integrity="sha384-JZR6Spejh4U02d8jOt6vLEHfe/JQGiRRSQQxSfFWpi1MquVdAyjUar5+76PVCmYl" crossorigin="anonymous"></script>
</body>
</html>