1. I-94 is a form denoting the Arrival-Departure Record of particular foreigners used by U.S. Customs and Border Protection (CBP). U.S. Citizenship and Immigration Services (USCIS). https://i94.cbp.dhs.gov/I94/request.html
is the website. You will have to select the Radio button of YES, I understand. Then submit.
It redirects you to the I-94 form where you will have to fill out your details and an I-94 number is generated for the travel records to USA. This number will be linked to your passport and will not change.
2. There is no need to get I-94 before you enter USA. No one asks to show while entering US but after you come to your school, you will have to submit a copy to your school for their records. And they will guide you with the process.