$formBuilder
$formBuilder : \Symfony\Component\Form\FormFactoryInterface
buildForm() : null
in this function you add all the fields you need for your Form.
Form this you have to call add method on $this->formBuilder attribute :
$this->formBuilder->add("name", "text") ->add("email", "email", array( "attr" => array( "class" => "field" ), "label" => "email", "constraints" => array( new \Symfony\Component\Validator\Constraints\NotBlank() ) ) ) ->add('age', 'integer');