Basic marking for creating a standard subscribe form looks the following way:

<form data-form-output="form-output-global" data-form-type="subscribe" method="post" action="bat/rd-mailform.php" class="rd-mailform form-inline">
  <div class="form-group">
    <label for="contact-email" class="form-label">E-Mail</label>
    <input id="contact-email" type="email" name="email" data-constraints="@Email @Required" class="form-input">
  </div>
 
  <button type="submit" class="button button-primary">Send</button>
</form>