Having US Preclearance means going through US Customs and Immigration before you get on your departing airplane instead of after you arrive in the United States. Upon departure from the Bahamas via LPIA (Nassau's International Airport) or Grand Bahama International Airport check-in procedures are as normal with any International airport. After check-in you proceed to an area set aside in the airport that's considered US territory. There, you go through immigration and customs with US Customs and Border Protection (CBP) officials staffing the area. Once completed you enter the gate area where you wait for your flight. That means when you do arrive in the US there are no formalities left-you can collect your bags from baggage claim and proceed out the terminal if this is your final destination or continue to your connecting gate!