On first sight CO09 is a little tough to read/understand.
The right column "*** ATP quantity" shows you the quantity that you is available and can be given (promised) to a customer or internal requester.
Frankly spoken, you either have something, or you have nothing (0), but less than nothing (quantity with minus) means you promised somebody that he can get X quantity (confirmed), but then you gave the quantity to someone else. So you are in trouble.
the first column shows the minus sign to know that is is a reduction, while a positive number indicates that you will receive quantity.
The middle column (confirmation) is of course positive, as it just shows what you confirmed.