Saving Form Fields

I'm new to module development and I'm wondering where I would save data inputted from the user for my custom field. I have my own databases table structure so I'll be doing my own sql queries, but I'm really unsure how and where I can actually get the input information when the user hits the submit button. Is it in the hook_widget for the submit operation? If that's the case, when I save something and print out the contents of $field and $items, I don't get anything returned from those arrays so I don't know how to access the data being submitted. Is there an existing module I can refer to as an example?

This is what I have for my code so far. Basically I'm building a custom field for adding rows of ingredients, with 3 columns.

<?php

function ingredients_field_settings($op, $field) {

    switch ($op) {
    
    case 'form':
        return form;
        
    case 'callbacks':
        return array(
            'view' => CONTENT_CALLBACK_DEFAULT
          );
    }
}



function ingredients_field($op, &$node, $field, &$items, $teaser, $page) {

}


function ingredients_widget_info() {
    $info = array(
        'ingredients' => array(
            'label' => t('Ingredients'),
            'field types' => array('ingredients'),
        ),
    );

  return $info;
}

function ingredients_widget_settings($op, $widget) {
  switch ($op) {
    case 'form':
        $form = array();
        $form['num_rows'] = array(
            '#type' => 'textfield',
            '#title' => t('Default number of rows'),
            '#default_value' => $widget['num_rows'] ? $widget['num_rows'] : 10,
            '#size' => 3,
            '#maxlength' => 3,
            '#description' => t('Set the number of ingredient input lines to be displayed by default (user can dynamically add lines later on as needed).'),
            '#required' => TRUE,
        );
      return $form;

    case 'validate':
        if (!isset($widget['num_rows']))
            form_set_error('num_rows', t('You must specify a default number of ingredient input lines  to display to the user'));
        break;

    case 'save':
        return array('num_rows');

    case 'callbacks':
        return array('default value' => CONTENT_CALLBACK_CUSTOM);    
  }
}


function ingredients_widget($op, &$node, $field, &$items, $delta = NULL) {

    switch ($op) {
        case 'form':

            $defaultNumRows = $field['widget']['num_rows'];

            $form = array();
                
            $form['ingredient'] = array (
                '#type' => 'fieldset',
                '#title' => $field['widget']['label'],
                '#collapsible' => TRUE,
                '#collapsed' => FALSE,
                '#tree' => TRUE,
                '#theme' => 'ingredients_form_fieldgroup',
                '#attributes' => array('class' => 'container-ingredient'),
            );
            $form['ingredient']['num_rows'] = array (
                '#value' => $defaultNumRows,
            );
              
            for ($i = 0; $i < $defaultNumRows; $i++) {
                $form['ingredient']['values'][$i] = build_ingredients_input_fields();
            }
        
            return $form;
        
        case 'submit':
            /* database insert queries here? */
            db_query("INSERT INTO {ingredient_groups} (
                            name)
                      VALUES ('%s')",
                               $items['values'][0]['ingredient_name']);   /* unable to see user input data */

            return $form;
    
      return;
  }
}

// Create form values and attributes
function build_ingredients_input_fields() {

  include_once(drupal_get_path('module', 'ingredients') .'/ingredients.inc');

    $form['quantity'] = array(
        '#type' => 'textfield',
        '#maxlength' => 8,
        '#size' => 8,
    );    
    
    $form['units'] = array(
        '#type' => 'select',
        '#options' =>  array('option 1', 'option2'), /*ingredient_get_units(), */
    );  
    
    $form['ingredient_name'] = array(
        '#type' => 'textfield',
        '#size' => 64,
        '#maxlength' => 128,
    );              
    return $form;
}

/**
 *  Theme entire ingredient field form.
 *
 *  Display inline rows of input fields for quantity, units, and ingredient names
 *
 */
function theme_ingredients_form_fieldgroup($form) {

    foreach($form as $line => $element) {

        if ($line == 'values' && is_array($element)) {            
            for ($i = 0; $i < $form['num_rows']['#value']; $i++) {                    
                $rows[] = array(
                    drupal_render($element[$i]['quantity']),
                    drupal_render($element[$i]['units']),
                    drupal_render($element[$i]['ingredient_name'])
                );
            }
        }
    }
    
    $header = array(t('Quantity'), t('Units'), t('Ingredient'));
    $output = theme('table', $header, $rows);

/*    $output .= drupal_render($form);*/
    
    return $output;
}

?>

Another question I have is what am I supposed to implement in my hook_field()? It seems like everything I need is all in my widget functions.

Any help would be greatly appreciated!

Thanks.