You can type the product name or code to get the suggestion and the select the suggestion or just scan the barcode with your barcode scanner to add product to the order list. If there is only 1 suggestion for your typed characters, then it will automatically have added to the order list. If you have scanned the barcode with option, the order item option will automatically set to the scanned barcode option.
Add product to order list and the totals will be automatically stick top and bottom once the order list reached the number that you have in settings for Product counts to fix for barcode input.