Form declaration (from menu to submit)

/*
 * Implementation of hook_menu()
 */
function mysnippet_menu() {
  $items['mysnippet/myform'] = array( 
    'title' => 'A basic form',
    'description' => 'Example to create a form, validate and handle submitted values',
    'page callback' => 'drupal_get_form', // we want a form
    'page arguments' => array('mysnippet_create_form'), 
    'access arguments' => array('basic permission'), //only users with this permission enabled have access to the form otherwise use 'access callback' => TRUE,
    'type' =>  MENU_CALLBACK, // won't be displayed in any menu you could use MENU_PRIMARY_LINKS
  );
  return $items;
}
 
/*
 * Implementation of hook_form()
 */
function mysnippet_create_form($form, &$form_state) {
  //the documentation of the form API can be found here: http://drupal.org/node/1702548
  $form['name'] = array(
    '#type' => 'textfield', // we define a simple text field
    '#title' => 'What is your name?',
    '#description' => 'you can not enter here Drupal...',
    '#required' => TRUE, //we do not want an empty value
    '#default_value'=> variable_get("basic_name",""),
  );
  return $form;
}
 
/*
 * Implementation of hook_form_validate()
 */
function mysnippet_create_form_validate($form, &$form_state)  {//submitted values are hold in $form_state['values']
  // dpm($form_state['values']) //to see them all
  if($form_state['values']['name']=='Drupal') { // we verify that the name is not Drupal
    form_set_error('name', 'You can not use Drupal here...'); // if yes we set an error on the field name
  }
}
 
/*
 * Implementation of hook_form_submit()
 */
function mysnippet_create_form_submit($form, &$form_state)  {
  //we use variable_set to record our values in the database (table variable)
  variable_set('basic_name', $form_state['values']['name']);
 
  //we display a confirmation message
  drupal_set_message('Your settings have been saved !', 'status');
}