Answer:
Non-commissioned officers, "noncoms" for short, are men who are not actual officers, but who do have control, charge, or supervision over other men. Noncom ranks are some specialist ranks, corporals, sergeants, staff sergeants etc.
Commissioned officers are "brass", Second Lieutenant, Lieutenant, Captain, Major, etc., and who have command over units of men, platoons, batteries, companies, troops, brigades, corps, etc.; or, over specific missions or deployments.
There is a third class of officer in American ranks call the Warrant officer. Warrant officers have the command authority of a noncom, but the rank equivalent of juniro to mid-grade officers. It is traditional in the US Army for example to defer to the knowledge and authority of a warrant officer in his area of specialty regardless of ones rank due in no small part to the specialized training and job responsibility they receive.