I’m newbie on Drupal and I try to set an validation and submit the custom user registry form but I try and validation not call.

function mymodule_theme(&$  existing, $  type, $  theme, $  path){    $  hooks = array();    // Make user-register.tpl.php available   $  hooks['user_register_form'] = array(     'render element' => 'form',     'path' => drupal_get_path('theme', 'mymodule') . '/templates',     'template' => 'user-register',     'preprocess functions' => array('mymodule_preprocess_user_register_form'),   );   return $  hooks;  }  function mymodule_preprocess_user_register_form(&$  vars) {    $  vars['title'] = 'Registro de candidatas';   $  vars['message_welcome'] = '<p>Ingresar tu correo electrónico para iniciar este proceso. Asegúrate de tener abierto dicho correo para recibir las notificaciones y realizar de manera inmediata las indicaciones que recibas.</p>';    //Shortens the form variable name for easier access   $  form = $  vars['form'];     $  form['account']['mail']['#attributes'] = array(     'placeholder' => 'Escribe tu correo electrónico',     'class' => array(       'mymodule-form-email-input'     )   );   $  form['account']['mail']['#title_display'] = 'invisible';   $  form['account']['mail']['#description'] = '';    $  form['account']['pass']['pass1']['#title_display'] = 'invisible';   $  form['account']['pass']['pass1']['#attributes'] = array(     'placeholder' => 'Escribe una contraseña',     'class' => array(       'mymodule-form-email-input'     )   );    $  form['account']['pass']['pass2']['#title_display'] = 'invisible';   $  form['account']['pass']['pass2']['#attributes'] = array(     'placeholder' => 'Vuelve a escribir contraseña',     'class' => array(       'mymodule-form-email-input'     )   );    $  vars['mail'] = render($  form['account']['mail']);   $  vars['pass'] = render($  form['account']['pass']);   $  vars['captcha'] = render($  form['captcha']);  }  function mymodule_user_register_form_alter(&$  form, &$  form_state, $  form_id) {    $  form['account']['mail']['#field_prefix'] = '';   $  form['#validate'][] = 'mymodule_user_register_form_validate';  }  function mymodule_user_register_form_validate(&$  form, &$  form_state) {    drupal_set_message(t('AN ERROR OCURED'));    if ($  form_state['values']['mail'] !== '') {     form_set_error('mail', t('Escribe un correo electrónico'));   } else {     if(valid_email_address($  form_state['values']['mail'])) {       form_set_error('mail', t('Email invalido'));      }   }    if ($  form_state['values']['pass']['pass1'] !== '') {     form_set_error('mail', t('Escribe una contraseña'));    }    if ($  form_state['values']['pass']['pass2'] !== '') {     form_set_error('mail', t('Confirma tu contraseña'));    }    if ($  form_state['values']['pass']['pass1'] !== $  form_state['values']['pass']['pass2']) {     form_set_error('mail', t('La contraseñas no coinciden'));    }    if (!$  form_state['values']['sendgift']) {     form_set_error(NULL, '', TRUE);     drupal_get_messages();   }  } 

Something I have wrong? I look on documentation and I found few details on registration. I read about hook_form_alter() and hook_preprocess_form() but it’s confusing to me.

Thanks