What are the different ranks in military jobs?

I'm trying to understand the military structure and how job ranks work. Can someone explain the different ranks one might encounter in a military career, and how advancement through these ranks typically occurs?

There are different ranks systems in each branch of the military in the United States, but they can generally be divided into two categories: enlisted ranks and officer ranks.

Enlisted personnel make up the majority of military personnel and do much of the hands-on work, although they can rise to leadership roles. The initial rank in most branches is known as a Private (USA/USMC), Seaman Recruit (USN), or Airman Basic (USAF). Progression continues to Private First Class, Specialist/Corporal, and then into the non-commissioned officers ranks such as Sergeant and Staff Sergeant, all the way to Sergeant Major.

Officers usually have higher levels of education (typically at least a bachelor's degree) and are responsible for leading large groups of enlisted personnel and planning missions. Officer ranks begin with Second Lieutenant (in the Army, Air Force, and Marine Corps) or Ensign (in the Navy and Coast Guard), and progress to First Lieutenant, Captain, Major, and so on, up to General (in the Army, Air Force, and Marine Corps) or Admiral (in the Navy and Coast Guard).

Advancement through the ranks depends largely on time in service, performance evaluations, and, at higher levels, competitive selection for promotion. For enlisted personnel, initial promotions come relatively quickly, while later promotions become more competitive. Officers are generally evaluated for promotion every few years with less than 100% promotion rates.

It's also worth noting that some positions, such as doctor or chaplain, carry a rank but exist somewhat outside of the traditional hierarchical structure.

Keep in mind that this is a very simplified overview and the military rank structure can be complex. You also have Warrant Officers, who are specialists and fall somewhere between enlisted and officer ranks. And it can differ between branches, so it's important to research the specifics of the branch you're interested in.