NCO or Non-Commissioned Officer and Commissioned Officer are two terms in the military, referring to the status of every military personnel. Non-commissioned officers are soldiers in the military who have not received a direct conveyance of authority from the sovereign government, and as such, they can't issue commands except to the low ranking soldiers under them, especially during training and other military actions. Sergeant and corporal are two common examples of positions for non-commissioned officers.
On the other hand, a commissioned officer is a military officer who has received a commission from the sovereign government; and, as such, has the power to issue commands and orders to carry out certain duties and responsibilities that are tied to such position or office.
Commissioned officers are high ranking officers in the military. They set policies and programs to be carried out by the non-commissioned officers. They also get higher pay compared to the non-commissioned officers.