<?php

  function my_ajax_menu() {
    $items = array();

    $items['admin/config/my_ajax_learning'] = array(
      'title' => t('my ajax learning'),
      'page callback' => 'my_ajax_form',
      'access callback' => true,
      'menu_name' => 'management',
    );

    return $items;
  }

  function my_ajax_form() {
    return drupal_get_form('ajax_form_b');
  }

  function ajax_form_b($form_id, $form_state) {
    $form = array();

    $form['my_learning_fieldset'] = array(
      '#type' => 'fieldset',
      '#title' => t('learning ajax'),
      '#description' => t('my learning ajax field set description'),
      '#tree' => true,
    );

    $form['my_learning_fieldset'][my_learning_checkbox'] = array(
      '#type' => 'radios',
      '#title' => t('learning ajax'),
      '#description' => t(	'learning ajax again'),
      '#options' => array(
        'a' => 'a',
        'b' => 'b',
        'c' => 'c',
      ),
      '#ajax' => array(
        'callback' => 'learn_ajax_here',
        'wrapper' => 'put_ajax_here'
      ),
    );

    $form['my_ajax_content'] = array(
      '#type' => 'textfield',
      '#prefix' => '<div id = \'put_ajax_here\'>',
      '#suffix' => '</div>',
      '#description' => 'thank you',
    );

  return $form;
  }

  function learn_ajax_here($form, &$form_state) {
    drupal_set_message('<pre> ' . print_r($form_state['values'], true) . '</pre>');

    $form['test'] = array(
      '#title' => t('test'),
      '#description' => t('test'),
      '#type' => 'select',
      '#options' => $form_state['values']['my_learning_checkbox'],
    );

    return $form['test'];
  }