Simple Form Validation using php | Learning Curve- Perfect Tutorial for the beginers

<?php
if(isset($_POST['submit']))
{
//accesing the user entered details

$username=trim($_POST['name']); //trim function is using for remove the spaces from the start and end of the string where customers entered.
$email=trim($_POST['email']);
$phone=trim($_POST['phone']);
if(empty($username) && empty($email))
{
echo "All fields are compulsory";
}
else
{
header("Location: test.php");
}
}
?>
<html>
<head>
<title>Simple Contact Form</title>
</head>
<body>
<form id="myform1" method="post" action="test.php"> <br />
Employee Name  : <input type="text" name="name"  value="" /> <br />
Email   : <input type="text" name="email"  value="" /> <br />
Phone   : <input type="text" name="phone"  value="" /> <br />

<p><input type="submit" name="submit" class="button" value="Submit" /></p>

</form>

</body>

</html>

<?php

if(isset($_POST['submit']))

{

//accesing the user entered details

$username=trim($_POST['name']); //trim function is using for remove the spaces from the start and end of the string where customers entered.

$email=trim($_POST['email']);

$phone=trim($_POST['phone']);

if(empty($username) && empty($email))

{

echo "All fields are compulsory";

}

else

{

header("Location: test.php");

}

<html>

<head>

<title>Simple Contact Form</title>

</head>

<body>

Employee Name : <input type="text" name="name" value="" /> <br />

Email : <input type="text" name="email" value="" /> <br />

Phone : <input type="text" name="phone" value="" /> <br />

</form>

</body>

</html>