Passport
Your passport is the basic travel document issued by your government. While you are in the U.S., your passport must be valid for at least 6 months into the future. Your passport can be renewed at your government's embassy in Washington, D.C. It must be valid if you plan to leave and re-enter the U.S.
Form I-20
Immigration form I-20 is a Certificate of Eligibility for non-immigrant (F-1) student status. It is the document issued by academic institutions that students use to obtain F-1 visas abroad, to re-enter the U.S. and to transfer from one school to another. Your signature on the I-20 means you understand the DHS regulations and accept them.
Upon entry into the U.S., the DHS inspector will take the top copy of your I-20. The bottom copy (Form I-20 ID – student copy) will be returned to you. Keep this with your passport.
In the case of transfers or continuations, the school will give you the student copy of your new I-20 and mail the top copy to the DHS processing center.
Your I-20 is valid for the time period indicated on the form only if you maintain status. Your I-20 becomes invalid despite the expiration date if you are "out of status."
F-1 Visa
A visa is an official document issued by a consulate overseas allowing a foreign national to apply for admission into the United States. The visa can be either a multicolored stamp or a computerized document with the picture of the foreign national. It includes your name, visa classification (F-1), place and date of issue, expiration date, and the number of times you are permitted to enter the U.S. (S = single entry, M = multiple entries).
Once you have entered the U.S., the expiration date on your F-1 visa is no longer important for initial entry purposes.
Form I-94
This is a small white arrival/departure card that visitors receive when they enter the U.S. This card should be attached to your passport. It contains a unique eleven-digit number in the upper left hand corner, the name of the individual admitted, their birth date, citizenship, date of admission, and the immigration status given at the port of entry.
Students with F-1 visas have "D/S" written on their I-94. "D/S" means "duration of status" and indicates students can remain in the U.S. for as long as they are studying full-time in educational institutions and maintaining status.
Upon entry into the U.S., the DHS inspector will take the I-94 Arrival card for processing and staple the I-94 Departure Card into your passport.
When you leave the U.S., you must surrender your I-94 Departure Card. You receive a new I-94 arrival/departure form every time you enter the U.S.
Your I-94 departure is proof that you have legally entered the country. If you lose this card, you must complete Form 1-102 (application by non-immigrant alien for replacement of arrival document).