101st Port Marine Company was the unit he was assigned to when discharged - may or may not have been the unit he served with overseas and probably wasn't. "GO #33 WD 1945" (War Department General Orders Number 33, 46 & 40 of 1945), etc. are, respectively, the official bases for the campaign credits indicated. The EAME Medal is visual evidence of his service in that theater of operations and the bronze service stars are devices worn on the ribbon of the medal as visual evidence of participation in the campaigns indicated (as you may now realize, the government, especially the military, was - and is - "big" on visual evidence; symbolism over substance).
Technician Fourth Grade (also expressed T4, T/4, Tec4, Tech4, etc.) was a specialist rating that drew the same base pay as a "buck" sergeant. There were different types of riggers: duties may have included tying down materiel and equipment on board ship; may been a parachute rigger (packed or "rigged" parachutes - although this was usually specified). No way to tell specifically from scant information on a discharge or summary of service. Only way to be certain is to access records.