You talked with a US Customs and Border Protection customs officer when you first arrived in the US. You most likely had to gather your luggage and may have shown your I-20 form and passport. You may be asked questions about your educational plans. They typically ask if you're carrying fruit, meat, or other prohibited items into the U.S. If the customs officer does not believe that you intend on being a fulltime student, you could be asked to immediately leave the US even though you have an I-20. Almost all students though are approved for entry to the US. You will receive an I-94 form (admission record).