Asked by an anonymous Tumblr user.
If you are flying within the U.S., you do not need to fill out any forms. There are forms that apply to international travel.
Each individual traveling to the U.S. from another country must complete a customs declaration form. If you’re traveling with immediate family members, then you only need to fill out one form per family.
If you are not a citizen or permanent resident and are traveling with a Visa, then you will also need to fill out an Arrival/Departure Record (Form I-94). Travelers who obtained authorization to enter the U.S. via the Electronic System for Travel Authorization do not need to complete the Arrival/Departure Record. Learn more about entering the U.S. as an international visitor.
After your flight lands in the U.S., you will present the form(s) and be inspected by a U.S. Customs and Border Protection officer. They prevent terrorists, people with outstanding criminal warrants, narcotics, agricultural pests, and smuggled goods from entering the United States.