How do I use $form_state to return data from the from submission handler to the form builder? I am trying to populate a data based on $form_state right after submission.
What I am trying to do is to populate a form that takes a keyword and passes it to a function that gets the result from another site.

I can use $form_state['values']['keyword'] in MYMODULE_form_submit() but not in MYMODULE_form_page().

How can I achieve this?

function MYMODULE_menu() {
  // Module settings.
  $items['MYMODULE'] = array(
    'title' =&gt; 'MYMODULE',
    'description' =&gt; 'MYMODULE',
    'page callback' =&gt; 'MYMODULE_form_page',
    'page arguments' =&gt; array('MYMODULE_form'),
    'access callback' =&gt; TRUE,
  );
  return $items;
}

function MYMODULE_form($form, &amp;$form_submit){
  $form['kname'] = array(
    '#title' =&gt; t('What would you like to search:'),
    '#type' =&gt; 'textfield',
    '#required' =&gt; TRUE,
    '#description' =&gt; t('Please insert the keyword you whish to search for.'),
  );

  $form['submit'] = array(
    '#type' =&gt; 'submit',
    '#value' =&gt; 'Send',
  );

  return $form;
}

function MYMODULE_form_submit($form, &amp;$form_state) {
  $keyword = $form_state['values']['kname'];
  $op = MYMODULE_simple_page($keyword);

  return $op;
}

function MYMODULE_form_page($op) {
  $build = array(
    'header_text' =&gt; array(
      '#type' =&gt; 'markup',
      '#markup' =&gt; '&lt;p&gt;&lt;/p&gt;',
    ),
    'example_form2' =&gt; drupal_get_form('MYMODULE_form'),
    array(
      '#type' =&gt; 'markup',
      '#markup' =&gt; '&lt;p&gt;'. $op .'&lt;/p&gt;',
    ),
  );

  return $build;
}

function MYMODULE_simple_page($keyword) {
  // Query the external website.
  $data = drupal_http_request('API_ADRESS_JSON');

  // Decode JSON.
  $test = drupal_json_decode($data-&gt;data);
  $outitem = '';
  $output = '';
  // Loop through the array (converted from JSON) and view the list of the result as titles and images.
  if (isset($test)) {
    for ($i=0; $i&lt;count($test['images']); $i++) {
      $imageName = $test['images'][$i]['title'];
      $variables = array(
        'path' =&gt; $test['images'][$i]['thumbnail_path'], 
        'alt' =&gt; 'Test alt',
        'title' =&gt; 'Test title',
        'attributes' =&gt; array('class' =&gt; 'some-img', 'id' =&gt; 'my-img'),
      );
      $img = theme('image', $variables);
      $outitem .= '&lt;div class=image&gt;&lt;p&gt;&lt;strong&gt;'. $imageName .'&lt;/strong&gt;&lt;/p&gt; &lt;br&gt;&lt;p&gt;'. $img .'&lt;/p&gt; &lt;br&gt;&lt;/div&gt;';
    }
  }

  $output .= $outitem;

  return $output;
}
The only functions that get $form_state are form builders, form validation handlers, and form submission handlers. 

To say the truth, your code doesn't need to use MYMODULE_form_page(): You can simply use the form builder function.

function MYMODULE_menu() {
  // Module settings.
  $items['MYMODULE'] = array(
    'title' =&gt; 'MYMODULE',
    'description' =&gt; 'MYMODULE',
    'page callback' =&gt; 'drupal_get_form',
    'page arguments' =&gt; array('MYMODULE_form'),
    'access callback' =&gt; TRUE,
  );
  return $items;
}

function MYMODULE_form($form, &amp;$form_state) {
  $form['header_text' =&gt; array(
    '#markup' =&gt; '&lt;p&gt;&lt;/p&gt;',
  );

  $form['kname'] = array(
    '#title' =&gt; t('What would you like to search'),
    '#type' =&gt; 'textfield',
    '#required' =&gt; TRUE,
    '#description' =&gt; t('Please insert the keyword you whish to search for.'),
  );

  if (isset($form_state['MYMODULE_result'])) {
    $form['footer_text'] = array(
      '#markup' =&gt; '&lt;p&gt;'. $form_state['MYMODULE_result'] .'&lt;/p&gt;',
    );
  }

  $form['submit'] = array(
    '#type' =&gt; 'submit',
    '#value' =&gt; 'Send',
  );

  return $form;
}

function MYMODULE_form_submit($form, &amp;$form_state) {
  $keyword = $form_state['values']['kname'];
  $op = MYMODULE_simple_page($keyword);

  // Form submission handlers don't return any value.
  // If you need to return a value to the form builder, you should use the following code.
  $form_state['MYMODULE_result'] = $op;
  $form_state['rebuild'] = TRUE;
}