A duty is something you must do by virtue of your position and is a legal or moral obligation. For example, it is the supply sergeant's duty to issue equipment and keep records of the unit's supplies. It is the first sergeant's duty to hold formations, instruct platoon sergeants and assist the commander in supervising unit operations. It is the duty of the squad/section/team leader to account for his soldiers and ensure that they receive necessary instructions and are properly trained to perform their jobs.
A noncommissioned officer's duties are numerous and must be taken seriously. An NCO's duty includes taking care of soldiers, which is your priority. Corporals and sergeants do this by developing a genuine concern for their soldiers' well-being. Leaders must know and understand their soldiers well enough to train them as individuals and teams to operate proficiently. This will give them confidence in their ability to perform well under the difficult and demanding conditions of battle. Individual training is the principle duty and responsibility of NCOs. No one in the Army has more to do with training soldiers than NCOs. Well trained soldiers will likely succeed and survive on the battlefield. Well trained soldiers properly do the tasks their NCOs give them. A good leader executes the boss's decisions with energy and enthusiasm; looking at their leader, soldiers will believe the leader thinks it's absolutely the best possible solution.