hook_block

function hook_block($op = 'list', $delta = 0, $edit = array()) {
  if ($op == 'list') {
    $blocks[0] = array('info' => t('Mymodule block #1 shows ...'),
      'weight' => 0, 'status' => 1, 'region' => 'left');
      // BLOCK_CACHE_PER_ROLE will be assumed for block 0.
 
    $blocks[1] = array('info' => t('Mymodule block #2 describes ...'),
      'cache' => BLOCK_CACHE_PER_ROLE | BLOCK_CACHE_PER_PAGE);
 
    return $blocks;
  }
  else if ($op == 'configure' && $delta == 0) {
    $form['items'] = array(
      '#type' => 'select',
      '#title' => t('Number of items'),
      '#default_value' => variable_get('mymodule_block_items', 0),
      '#options' => array('1', '2', '3'),
    );
    return $form;
  }
  else if ($op == 'save' && $delta == 0) {
    variable_set('mymodule_block_items', $edit['items']);
  }
  else if ($op == 'view') {
    switch($delta) {
      case 0:
        $block = array('subject' => t('Title of block #1'),
          'content' => mymodule_display_block_1());
        break;
      case 1:
        $block = array('subject' => t('Title of block #2'),
          'content' => mymodule_display_block_2());
        break;
    }
    return $block;
  }
}