The average cost refers to the amount that will be spent to make sure that specific processes and items will be produced or appropriately offered to the general public. Marginal cost applies to the extra expenses that are needed to ensure that a particular unit will become available. Take note that the average price would need the amounts of the different costs then, it will be divided by the number of items that were computed.
That is the only time when the total average cost will become known. These things are needed in business because, without proper knowledge about these things, the company has a higher chance of incurring extra expenses that they could have avoided.