Drupal 7 Basic form with submit handler

Bellow code tells about the basic form submit in drupal7

<?php
function my_module_menu() {
  $items = array();
  $items['my_module/form'] = array(
    'title' => t('My form'),
    'page callback' => 'my_module_form',
    'access arguments' => array('access content'),
    'description' => t('My form'),
    'type' => MENU_CALLBACK,
  );
  return $items;
}

function my_module_form() {
  return drupal_get_form('my_module_my_form');
}

/*
  # Sample registration form 
*/
function my_module_my_form($form_state) {
  $form['name'] = array(
    '#type' => 'fieldset',
    '#title' => t('Name'),
    '#collapsible' => TRUE,
    '#collapsed' => FALSE,
  );
  $form['name']['first'] = array(
    '#type' => 'textfield',
    '#title' => t('First name'),
    '#required' => TRUE,
    '#default_value' => "First name",
    '#description' => "Please enter your first name.",
    '#size' => 20,
    '#maxlength' => 20,
  );
  $form['name']['last'] = array(
    '#type' => 'textfield',
    '#title' => t('Last name'),
    '#required' => TRUE,
  );
  $form['year_of_birth'] = array(
    '#type' => 'textfield',
    '#title' => "Year of birth",
    '#description' => 'Format is "YYYY"',
  ); 
  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => 'Submit',
  );
  return $form;
}

function my_module_my_form_validate($form, &$form_state) {
    $year_of_birth = $form_state['values']['year_of_birth'];
    if ($year_of_birth && ($year_of_birth < 1900 || $year_of_birth > 2000)) {
      
  form_set_error('year_of_birth', 'Enter a year between 1900 and 2000.');
    }
}

 function my_module_my_form_submit($form, &$form_state) {
    drupal_set_message(t('The form has been submitted.'));
}

?>