Another important question is what level of ball do you want to work? Getting into recreation/park league ball has different requirements from intramural and from high school ball.
Assuming you are looking to do high school ball, the basic process usually (again, it varies from place to place) involves registering with your state office, and joining an officials association (called a board in many places). There may be some classes to take, which will benefit you greatly. There is often a test to pass. You will need to be familiar with the rule set for the level you'll be calling, and with the mechanics used by the group you'll officiate with.
All pretty generic information, I know. I would expect some folks from Philly and from NJ to be by soon enough to share more specifics.
Good luck and welcome to the glamorous world of basketball officiating.
