Drupal Forms

Basic structure:

  function my_form($form_state) {
    $form['submit'] = array(
      '#type' => 'submit',
      '#value' => t('Save'),
    );

    return $form;
  }
  
  function my_form_validate($form, &$form_state) {
  }

  function my_form_submit($form, &$form_state) {
  }

  print drupal_get_form('my_form');

Adding Form Functionality:
Uploading files:

    $form['#attributes'] = array('enctype' => "multipart/form-data"); 
    $form['image'] = array(
      '#type' => 'file',
      '#title' => t('Upload a new File'),
      '#description' => t('Select a file to upload into the knowledge base.')
    );

Read a submitted value

$form_state['values']['var_name'];

Returning messages

drupal_set_message("Thank you for submitting your post.");

form_set_error('var_name', 'You must enter a non-empty value as the new category name.');

Update a form after submitting it

$form_state['rebuild'] = TRUE;