each dormitory has its own address. Call housing to ask for yours. i.e. Hedrick Hall is 250 De Neve Dr. Box # **** Room 7** Los Angeles CA 90024
You pick it up on the bottom floor, they have a receiving area where all the mail goes and you show them your ID. They'll email you when it gets there.
No, your box number is different from your room number. It matters more for the smaller pieces of mail. They'll request it for that, but for packages you should be okay with room number. (The numbering for the boxes is different from rooms, at least in Halls).