Enlisted ranks in the Army (and I think most other US branches of the military too) are graded E1 through E9, E1 being Private, where you start, no authority, can't wipe their own ass without help, generally just completing basic training and AIT is enough to get you promoted to E2, Private 2nd Class, then about 6 months later you get promoted to E3, Private First Class or PFC. E4 is Specialist, the highest rank before ranks become NCOs or (Non-Commissioned Officers), E5 is Sergeant (SGT), E6 is Staff Sergeant (SSG), E7 is Sergeant First Class (SFC), E8 is Master Sergeant (MSG) or First Sergeant (1SG), and E9 is Sergeant Major (SGM) or Command Sergeant Major (CSM).

Generally (there are always exceptions to the rule) SGT are team leaders in charge of 2-4 E1-E4s, SSG's are squad leaders in charge of 3-4 E5's, SFC are are Platoon Sergeants in charge of 3-4 E6's

However working in a jail we also had positions that granted us different authority. For example, in the jail when I was working the Control Booth, even as an E4, I had authority to force even E9s to wait if I needed to for the safe operation of the jail. (Granted this would never happen, as anyone that high up in rank would have the whole facility partially locked down so there would be no inmate movement while they were there, so there would literally never be an instance where someone like that would have to wait, but if circumstances resulted in someone like that maybe showing up unannounced or what not, its very possible they would have to wait behind a door while an area of the facility had inmate movement since my position in the Control Booth and the requirements of a jail gave me specific requirements that even an E9 or General couldn't overrule).

A friend of mine got written up by an E6 Chef from the prison kitchen, that he made wait 2 minutes because of a large movement of inmates so by procedure he could not open the gate the E6 was behind. Our Platoon Sergeant (E7/SFC) got that write up, made a jerking off motion, tore it up and threw it away.