Custom module - form

[WeeklyJr]

Hi, I'm writing a custom module in Prestashop 1.7.5.2 and need to have a form. I've created a separate tab for my module and on the new page I have a table. When I want to add a new record I have a form and it shows correctly. Unfortunately, when I submit filled/blank form I get an error: access to undeclared static property $definition. I have a $definiton variable in my model, but somehow it still doesn't work. Here it is:

 /**
     *  @see ObjectModel::$definition
     */
    public static $definition = array (
        'table' => 'p_c',
        'primary' => 'id_p_c',
        'fields' => array(
            'id_p_c' => array('type' => self::TYPE_INT),
            'name' => array('type' => self::TYPE_STRING),
            'start' => array('type' => self::TYPE_DATE, 'validate' => 'isDate'),
            'end' => array('type' => self::TYPE_DATE, 'validate' => 'isDate'),
        ),
    );

And here is how I create the form in a controller:

public function renderForm() {
        $this->fields_form = array(
            'legend' => array(
                'title' => Context::getContext()->getTranslator()->trans('My module'),
                'icon' => 'icon-ticket'
            ),

            'input' => array(
                array(
                    'type' => 'text',
                    'label' => Context::getContext()->getTranslator()->trans('Name'),
                    'name' => 'name',
                    'required' => true,
                    'col' => 4,
                ),
                array(
                    'type' => 'date',
                    'label' => Context::getContext()->getTranslator()->trans('Start'),
                    'name' => 'start',
                    'required' => true,
                    'col' => 4,
                ),
                array(
                    'type' => 'date',
                    'label' => Context::getContext()->getTranslator()->trans('End'),
                    'name' => 'end',
                    'required' => true,
                    'col' => 4,
                ),
                array(
                    'type' => 'text',
                    'label' => Context::getContext()->getTranslator()->trans('Percentage'),
                    'name' => 'percentage',
                    'required' => true,
                    'col' => 4,
                ),
                array(
                    'type' => 'checkbox',
                    'name' => 'all_users',
                    'col' => 4,
                    'values' => array(
                        'query' => array(
                            array(
                                'id' => 'on',
                                'name' => Context::getContext()->getTranslator()->trans('All users'),
                                'val' => 1
                            )
                        ),
                        'id' => 'id',
                        'name' => 'name',
                    ),
                ),
            ),
            'submit' => array(
                'title' => Context::getContext()->getTranslator()->trans('Save'),
            ),
        );

        return parent::renderForm();
    }

I've been looking for any solution, but nothing fits to this problem. I also can't find any tutorial how to create a form in a custom module - official docs doesn't help and I'm out of sources after hours spent on crawling the Net.

Any help is highly appreciated!