How to store data in database with Form API? I'm new to developing Drupal 7 modules, and I can't figure out why my custom module's form data is not stored in my database's table called 'media_skins'. 

I followed the info explained in Creating modules - a tutorial: Drupal 7.x but I can't get it working. What's wrong with my code?

Here's my code:

function media_skins_menu() {
  $items = array();
  $items['admin/config/content/media_skins'] = array(
    'title' =&gt; 'Media Skins',
    'description' =&gt; 'Configuration for Skins module',
    'page callback' =&gt; 'drupal_get_form',
    'page arguments' =&gt; array('media_skins_form'),
    'access arguments' =&gt; array('access administration pages'),
    'type' =&gt; MENU_NORMAL_ITEM,
  );

  return $items;
}

function media_skins_form($form, &amp;$form_state) {

  $form['media_skins_test'] = array(
    '#type' =&gt; 'textfield',
    '#title' =&gt; t('Test field'),
    '#size' =&gt; 20,
    '#maxlength' =&gt; 20,
    '#description' =&gt; t('Test info for the field.'),
    '#required' =&gt; FALSE,
  );
  return system_settings_form($form);
}

function media_skins_form_validate($form, &amp;$form_state) {
    // For now, I will no validate anything
}

function media_skins_form_submit($form, &amp;$form_state) {
  $form = db_insert('media_skins')-&gt;fields(
    array(
      'start_date' =&gt; $form_state['values']['media_skins_test'],      
    )
  )
  -&gt;execute();
  drupal_set_message('Data stored in database successfully'); 
}


Any help will be very appreciated.

EDITING THE SCENARIO

After reading your comments, I tried the following, but I get "Unexpected error, try it again":

function media_skins_form($form, &amp;$form_state) {
  $form['media_skins_test'] = array(
    '#type' =&gt; 'textfield',
    '#title' =&gt; t('Test field'),
    '#size' =&gt; 20,
    '#maxlength' =&gt; 20,
    '#description' =&gt; t('Test info for the field.'),
    '#required' =&gt; FALSE,
  );
  $form['submit'] = array(
    '#type' =&gt; 'submit',
    '#value' =&gt; t('Enviar'),
  );
  return $form;
}
To use your own form submit handler, you should not use system_settings_form in your form, instead just return your form.

If you are just going to save your value in your submit handler, go with system_settings_form. 
To get the values, use variable_get('your form field name'). In your case, you can use variable_get('media_skins_test');