I have a module installed. I want to add an additional submit handler in to submit function of the module. for example I can add additional submit handler to a function with the following code in drupal 6.

function test_form_alter(&$form, &$form_state, $form_id) {

  switch ($form_id) {
    case "form id":
      $form['#submit'][] = 'test_community_submit';
      break;
  }
}

function test_community_submit($form, &$form_state) {
  // Do some stuff here.
}

How can achieve the above functionality in drupal 7?

The difference between form_state['values'] VS form_state['input'] should really be included in at least one of these examples, as this functionality, as written, is misleading.

You can reference your data from the $form_state object, as displayed in these examples. Consider:

$form['title_field'] = array(
    '#type' => 'textfield',
    '#title' => t('My Title'),
  );

You can reference this value in the validation or other functions by accessing the $form_state array, as such:

$my_title_value = $form_state['values']['title_field'];

This is shown in several examples. *However,* if you pre-populate a form with a value, like so:

$form['title_field'] = array(
    '#type' => 'textfield',
    '#title' => t('My Title'),
    '#value' => 'My Title',
  );

then trying to get the value with the method above will return 'My Title' *instead* of the user-modified value. To get the modified value, in my experience, you must do it like so:

$my_title_value = $form_state['input']['title_field'];

This should return the user-supplied value you're more likely looking for. Note that using $form['title_field']['#value'] *also* returns the value *before* the user modified it. This is not obvious, and it would make sense to clarify this in the example module.

They are all out of order,
1 should become 01 2 should become 02 ect...

My experience has shown that spaces in the form element names will cause the entered values to be missing from the $form_state['values'] array. Refer to my comment at https://drupal.org/comment/8285811#comment-8285811.