When you enter the United States through a port of entry, a U.S. Customs officer will review your documentation and determine your eligibility for F-1 status. They will then stamp your passport and create a digital I-94 record which you can retrieve proof of through the CBP I-94 website or the CBP One™ mobile app (available from the iOS App Store and the Google Play Store). More information about the I-94 is available from the U.S. Customs and Border Protection website.
NOTE: The U.S. Customs and Border Protection (CBP) now automates the Form I-94 process at air, sea, and land ports of entry. A paper I-94 will no longer be provided at such ports except in limited circumstances. For more information, please review CBP’s I-94 Automation Fact Sheet.