If the customer ordered products, you can add them to the order by clicking on the Add to order button next to each product type. Products that are added create respective charges in the Charges section of the order.
If additional products need to be added to the order or if products that have been added need to be removed, you can do this from the Charges section.
If you want to add a separate pre-defined charge or a custom charge, click on the Add charge button.
Once you have finished, click on "Finished picking products" to move on to the next step. You can continue to the next step even if not all products have been picked in case you don't have some of the products in stock.