Do I have to manually confirm an order every time a new order is placed?

No. Confirmation is not needed from your side. If you have an item on the ONDC network and the quantity is more than zero, an order will automatically be created. If you’ve selected on network delivery method, the assigned delivery partner will fulfil the order. If you’ve selected off network delivery method, you’ll have to fulfil the order.
However, if you want to cancel the order, you’ll have to do it manually.