<?php defined('C5_EXECUTE') or die(_("Access Denied.")); ?>
<h2 class="page-title">Add Number</h2>
   <div class="entry">
      <div class="clear"></div>
      <form action="<?php echo $this->action('save')?>" method='POST'>
         <div class="form_group">         
            <label for="number">Number</label>
            <input type="text" name="number">
         </div>
          <div class="ccm-dashboard-form-actions-wrapper">
          <div class="ccm-dashboard-form-actions">
              <button class="pull-right btn btn-success" type="submit" ><?=t('Save')?></button>
          </div>
          </div>
      </form>

<?php 
namespace Concrete\Package\Invoicing\Controller\SinglePage\Dashboard\<MyPackage>\<MyDashboard>;
use \Concrete\Core\Page\Controller\DashboardPageController;
use Config;
use Loader;
class Add extends DashboardPageController {
   private $_db;
   public function view() {
      $this->_db = Loader::db();
   }   
   public function save() {
      $number = $this->post('number'); 
      print $number;
   }
}

www.example.com/index.php/dashboard/<MyDashboard>/add

www.example.com/index.php/dashboard/<MyDashboard>/add/save