As much as possible on long term amnesia, please this is urgent.

Dear Doctor,
I have many questions relating amnesia cause by severe trauma, therefore I'm asking what are the medical procedures in dealing with a severe trauma patient, like if coming from a car crash and into the emergency room. I'd like to know what happens to the patient, say if he or she heals from the injuries, what would be the norm in introducing the patient with the outside world? How does the brain react when amnesia occurs, does it wipe out the long term, short term, or both? Also how is this treated ongoing and out of the hospital? Please, elaborate for me. Thank you, so much.