The most senior military ranks, collectively called "flag ranks", include Generals, Lieutenant Generals, Major Generals and Brigadiers, have comparable seniority to Admirals and Commodores in the Navy. These ranks may have command of Armies, Corps, Divisions and Brigades
The other commissioned ranks in modern armies include Colonel, Lieutenant Colonel, Major, Captain and Lieutenant. They units they command, include Regiments, Battalions, Companies and Platoons.
Commissioned officers generally had military training at the University level.
Modern armies also employ various non-commissioned officers, including Sergeants, Corporals and warrant officers -- individuals who may be very skilled or experienced, but did not have military training at the University level. They may command units smaller than platoons, commonly called squads.
Privates are the most junior enlisted personnel in many modern armies.