1.SP 4 is rank, Specialist 4.E-4 (T) is Enlisted grade 4, temoprary.All rank is temoprary until the person has held the rank for a specific length of time, then it becomes permanent.He was a Corporal.
2.Army AUS means he was in the Army of the United States.He was a draftee.UNASGD means he was not assigned to a unit at time of separation.(DD-214 is Separation Papers.)
3.Reason and Authority, AR is an Army Regulation under which he was separated from Active Duty under.Probably his enlistment was over.
4.KMAG is Korean Military Advisory Group. 5700 Detachemtn is the Army Unit D is the company and Prov means that is was a provisional unit. aPO is Army Post Office.That was his military mailing address.
5.TFRD to USAR, he was transferred to the United States Army Reserve.At the time he entered the military he had an 8 year obligation, 2 active and 6 inactive.The DD-214 separated him from active duty and transferred him to a military district. (The State in which he lived.)