Yii2.0 uses Gii to generate code

Open Gii

config/web.php:

$config = [ ... ];
if (YII_ENV_DEV) {
    $config['bootstrap'][] = 'gii';
    $config['modules']['gii'] = 'yii\gii\Module';
}

Set YII_ENV_DEV in web/index.php:

defined('YII_ENV') or define('YII_ENV', 'dev');

If accessing from non-localhost, you need to make the following settings in the configuration file:

'gii' => [
    'class' => 'yii\gii\Module',
    'allowedIPs' => ['127.0.0.1', '::1', '192.168.0.*', '192.168.178.20'] // adjust this to your needs
],

Test:

http://hostname/index.php?r=gii