I work as a teacher in adult education and I have developed sites (using Google Sites) for all of our courses at my school. I would like to take our sites a bit further by embedding some HTML elements to them.
One of the things I would like to embed is a feedback form. Since I am new to coding I have been working for a few days trying to get the form to work but I cannot seem to get it to work.
I would really appreciate if you guys could help me figure out what the issue is.
I know it might be very cluttered but this is what I managed to put together using Google Material Design Lite (paste the code here to see it: https://codepen.io/pen/):
<html>
  <head>
    <!-- Material Design Lite -->
    <script src="https://code.getmdl.io/1.3.0/material.min.js"></script>
    <link rel="stylesheet" href="https://code.getmdl.io/1.3.0/material.indigo-pink.min.css">
    <!-- Material Design icon font -->
    <link rel="stylesheet" href="https://fonts.googleapis.com/icon?family=Material+Icons">
  </head> 
<body>    
  <div class="contact-form">
    <form id="contact-form" method="post" action="#">
      <div class="mdl-textfield mdl-js-textfield mdl-textfield--floating-label">
        <input name="name" type="text" class="mdl-textfield__input" id="name">
        <label class="mdl-textfield__label" for="name">Namn (frivligt)</label>
      </div>
      <br>
      <div class="mdl-textfield mdl-js-textfield mdl-textfield--floating-label">
        <input name="course" type="text" class="mdl-textfield__input" id="course">
        <label class="mdl-textfield__label" for="course">Kurs (frivligt)</label>
      </div>
      <br>
      <div class="mdl-textfield mdl-js-textfield mdl-textfield--floating-label">
        <textarea name="message" class="mdl-textfield__input" rows="7" id="message"></textarea>
        <label class="mdl-textfield__label" for="message">Meddelande</label>
      </div>
      <br>
      <input type="submit" class="mdl-button mdl-js-button mdl-button--raised mdl-js-ripple-effect mdl-button--colored" value="skicka">
    </form>
  </div>
</body>  
</html>
This is the PHP I have written which I have linked with under action="#" by uploading the php file to my github respiratory and linking to it with an URL. 
<?php
        if(isset($_POST['Submit'])) {
            $name = $_POST['name'];
            $course = $_POST['course'];
            $message = $_POST['message'];
            $mailTo = "name.lastname@domain.com";
            $headers = "From: Site Form Submission";
            mail($mailTo, $course, $message, $headers);
            header("Location: index.php?mailsend");
        }
?>
When I submit the form on the site a new tab opens in my browser that says 404 Invalid. When I go back to the site the entries in the form are still there. I have never used PHP before so I guess that is where the main issue lies.
 
    