// Users/test.ctp

echo $this->Form->create();
echo $this->Form->input('firstname');
echo $this->Form->end('Test');

// UsersController.php

class UsersController extends AppController {
    public function test() {
        if ($this->request->is('post')) {
            $this->User->set($this->request->data);
            if ($this->User->validates()) {
                pr('no errors');
            } else {
                pr($this->User->validationErrors);
            }
        }
    }
}
// UserModel.php

class User extends AppModel {

    public $validate = array(
        'firstname' => array(
            'between' => array(
                'rule' => array('between', 3, 50),
                'message' => 'Firstname must be between 3 and 50 characters long.',
            ),
            'notEmpty' => array(
                'rule' => 'notEmpty',
                'message' => 'You must provide first name!'
            )
        )
    );
}