contact.ctp

<h1>Best contact form evar</h1>
<?php
echo $this->Form->create($form);
echo $this->Form->input('name');
echo $this->Form->input('email');
debug($this->Form->isFieldError('email'));
debug($this->Form->error('email'));
echo $this->Form->input('text');
echo $this->Form->button('submit');
echo $this->Form->end();

UsersController.php

<?php
namespace App\Controller;

use Cake\Form\Form;
use App\Controller\AppController;

class UsersController extends AppController
{
      public function contact()
      {
        $form = new Form;
        $form->schema()
        ->addField('name', 'string')
        ->addField('email', 'string')
        ->addField('text', 'text');
        $form->validator()
        ->requirePresence('name')
        ->add('name', 'len', ['rule' => ['minLength', 10]])
        ->add('email', 'format', ['rule' => 'email']);

        if ($this->request->is('post')) {
            $valid = $form->validate($this->request->data);
            if ($valid) {
                $this->Flash->success('nice work!');
            } else {
                $this->Flash->error('nope');
            }
        }
        $this->set(compact('form'));
    }
}