A visa is an approval stamp that allows you to enter the United States. As an international student, you will hold an F-1 visa. International students are usually admitted to the US for the duration of status, meaning that you may stay in the US as long as you are a full-time student. As long as you maintain your immigration status and have a valid I-20, you may stay in the US, even if your F-1 visa expires while you are still studying. However, if you leave the US with an expired visa and plan to re-enter, you must obtain a new F-1 visa from an embassy abroad before returning to the US.
When you enter the US on an F-1 visa, you have F-1 visa status. You must follow all regulations associated with your F-1 visa in order to maintain your immigration status. More details about maintaining your immigration status will be covered during orientation.