Message In Drupal

It's easy to make message in drupal. If your form function is data_form($form, &$form_state), so your submit function is data_form_submit($form, &$form_state). What's the point? The point is that you add "_submit" on the for function for your submit function. Look this  code

// form function

function data_form( $form, &$form_state){

    // implement codes

}

// form submit function

function data_form_submit( $form, &$form_state){

    drupal_set_message( t('Your data has been saved successfully') );

}

Message In Drupal