How to create magento helper class?

Question

I have the following magento helper class.

class CommissionJunction extends Mage_Core_Helper_Data
{

    /**
     * Get SKU, quantity, price and discount amount for each product in a given order
     * @param object $order
     * @return array
     */
    private function _getOrderProductsList($order) {
        $orderItems = $order->getAllItems();
        $purchasedSkus = array();
        $count_orderItems = count($orderItems);
        for($i = 0; $i < $count_orderItems; $i++) {
            $purchasedSkus[$i] = array(
              'ITEM' => $orderItems[$i]['sku'],
                'QTY' => number_format($orderItems[$i]['qty_ordered'],0), // no decimals
                'AMT' => number_format($orderItems[$i]['price'],2) // 2 decimal places
                'DCNT' => number_format(abs($orderItems[$i]['discount_amount']),2) */
            );
        }
        return $purchasedSkus;
    }

    /**
     * Get the Universal Data (JSON) Object for Commission Junction.
     * This object contains the order details passed on to Commission Junction for reporting purposes
     * on the Checkout Success / Order Confirmation page.
     * Notes:
     *  - CID, TYPE AND CURRENCY are hard coded
     * @param string $orderId
     * @return JSON object Universal Data Object for Commission Junction $json_masterTmsUdp
     */
    public function getCommissionJunctionUdo($orderId) {
        $order = Mage::getModel('sales/order')->loadByIncrementId($orderId);
        $udo = array();
        $udo['CID'] = 'XXXX';
        $udo['TYPE'] = 'XXXX';
        $udo['CURRENCY'] = 'USD';
        $udo['OID'] = $orderId;
        $udo['DISCOUNT'] = number_format(abs($order->discount_amount),2);

        $order_coupon_code = $order->coupon_code;
        if(!is_null($order_coupon_code) && !empty($order_coupon_code)) {
            $udo['COUPON'] = $order_coupon_code;
        }

        $udo['PRODUCTLIST'] = self::_getOrderProductsList($order);       

        if(Mage::getModel('core/cookie')->get('aff_commissionjunction') == 'cjafflx') {
            $udo['FIRECJ'] = "TRUE";
        }
        else {
            $udo['FIRECJ'] = "FALSE";
        }

        $masterTmsUdo['CJ'] = $udo;
        $json_masterTmsUdo = json_encode($masterTmsUdo);

        return $json_masterTmsUdo;

    }       


}

And I found this site where they explain how to register a helper class

http://codegento.com/2011/02/creating-a-helper-class/

The only thing I dont know its:

1. Where in the magento structure should I add this php class?
2. Where is the config.xml I should edit?

Answer 1

User created classes should be placed in this folder:

app/code/community

Another issue, you should use the same naming convention for your class as Magento uses ie

MOduleNameSpace_ComissionJunction_Helper_Data

Also the config XML should be placed in your app/code/community/ MOduleNameSpace/ComissionJunction/etc folder