You can use this facility if you already know the Polybags product codes of the products that you wish to order.
If you have just clicked on the 'order by product code' link to the left, you will see that a new window has popped up prompting you to enter a product code and a quantity (if you can not see this window, click here to open it now).
When you enter the product code and the quantity you require and click the 'how much?' button, the details of the appropriate product will be shown. The 'Order by Product Code' window will remain open (you can find it on your task bar at the bottom of the screen) so that you can find your next product using the same method.