It is your permit allowing you to travel to a U.S. port of entry and to request entry in F-1 student status.
You might think of your visa as an entry key to the door of the U.S.
Once you have opened the door and entered, you do not need to worry about whether your visa is valid or expired unless you leave and plan to re-enter the U.S. In that case, you must have your key—a valid U.S. visa—to be able to reenter.
Even though your visa allows you to travel to a U.S. port of entry, it is a Department of Homeland Security (DHS), Customs and Border Protection (CBP) immigration inspector who determines your admission into, length of stay and conditions of stay in, the U.S.
Your visa is valid for a specified number of entries to the United States: one, two, or "multiple," i.e., any number, until the expiration date.
If you are a Canadian citizen entering the U.S. from within the Western Hemisphere, you are not required to have a passport or visa, but you must show your Form I-20 and proof of Canadian citizenship. more
If you renew your passport and still have a valid visa in your old one, you may continue to use the visa in your old passport to enter the U.S.
If you change your status in the U.S. and then travel, you must have a visa corresponding to your new status when you re-enter the U.S.
In order to obtain a new F-1 visa, you generally should apply at a U.S. embassy or consulate within your country of citizenship or nationality; it can not be renewed in the U.S.
Contact the embassy or consulate where you plan to apply in advance to ask about the specific procedures and requirements at that location.
It is possible to apply for a visa as a “third country national” in a country other than your home country, but you may experience problems not experienced in your home country.