A customs form is handed out to all travelers; however, only one form per family is required to be filled out. Normally, the head of the family is responsible for ensuring the declaration is accurate. After you are admitted into the U.S. and retrieve your bags from the baggage claim, you will proceed to the secondary inspection area (the customs checkpoint). Hand your customs declaration to the officer. Most of the time, the officer will point you to the exit and that will be it. If you are traveling by air to the U.S., many airports will provide two lanes: for those who have something to declare and those who have nothing to declare. Regardless of the lane you choose, customs officers still have the right to detain you and search your bags. Sometimes, the officer may ask you some routine questions and then let you go. The officer may refer you to an adjacent X-ray machine to have your bags inspected or may refer you for a manual search of your bags. Any search more intrusive than a bag search is rare and is usually indicated only if some sort of probable cause has been established through questioning or during the bag search to suggest suspicious activity. Random searches of luggage, either by X-ray or manually, can occur.
You can't bring meat or raw fruit or vegetables but you may bring cooked non-meats, such as bread. See APHIS for details. The U.S. Customs process is straightforward. Most articles that are prohibited or restricted in any other country are prohibited or restricted in the U.S. The only rule that is unique to America is that it is generally prohibited to bring in goods made in countries on which the U.S. has imposed economic sanctions: Cuba, Iran, North Korea (DPRK), Syria, and Myanmar (Burma).
Besides your personal effects, which will go home with you, you are allowed to import $200 of merchandise duty free, including 1 liter of alcohol (for those 21 and older only) and 1 carton of cigarettes. If you are bringing in more than $10,000 cash or its equivalent, you must declare it on your customs form and you will be given a special form to fill out; not declaring exposes you to a fine and possible seizure of that cash.
The U.S. possessions of American Samoa, Guam, the Northern Marianas Islands, & U.S. Virgin Islands are outside federal customs jurisdiction. Each imposes their own separate requirements. Travel between these regions and the rest of the U.S. requires a customs inspection. There are some differences (mostly larger) in duty exemptions for U.S. citizens returning from these destinations.