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

    sleep(2)
    header("Location: http://example.com/newsletters/create_newsletter.php?template=new");

    if(isset($_GET['template'])
    {
        echo "hello robert now you are working on the template";
    }
}

<?php

$template = "";

if(isset($_GET['template']))
{
    $template = $_GET['template'];
}


if(isset($_POST['submit']))
{
    sleep(2)
    $messagename = $_POST['messagename'];
    $subject = $_POST['subject'];
    header("Location: http://example.com/newsletters/create_newsletter.php?template=new");

    if(isset($_GET['template'])
    {
        echo "hello robert now you are working on the template";
    }
}
?>

<form method="post">
    <input type="text" name="messagename" value="">
    <input type="text" name="subject" value="">

    <input type="submit" name="submit" name="submit" class="btn btn-primary" value="Next Step">
</form>