What is the I-94 form and where can I get it?

The I-94 form is the Department of Homeland Security's arrival and departure record, also known as the Arrival/Departure Record Card. It is issued to individuals who are admitted to the United States, those adjusting status while in the country, those extending their stay, and others.

A U.S. Customs and Border Protection (CBP) officer typically attaches an I-94 form to a nonimmigrant visitor’s passport upon entry into the country. Your I-94 will include an “Admit Until Date,” which indicates when your visa status expires. Brazilian tourists are usually given a maximum stay of 180 days, and if they wish to stay longer, they must apply for a Status Extension or Change of Status.
You can obtain your I-94 on the DHS website: https://i94.cbp.dhs.gov/I94/#/home