Before traveling to the United States, it's worth knowing a few practical rules — from visa procedures to cultural customs. Entry and visa. Citizens of Poland and most EU countries use the Visa Waiver Program — you only need an online ESTA authorization ($21, valid for 2 years, stays up to 90 days). Apply at least 72 hours before departure at esta.cbp.dhs.gov. For longer stays or work you need a B1/B2 visa, F1 (student), J1 (exchange), H1B (work) — filed at the US consulate. Your passport must be valid for the entire duration of your stay. At the border, a CBP officer will ask about the purpose of the visit, address of stay and length — have your hotel address and return ticket ready. Currency and payments. US Dollar (USD), $1 = 100 cents. Credit cards (Visa, Mastercard, American Express) work practically everywhere, even for small purchases. Cash is useful for tips, food trucks and small fees. ATMs are on every corner, $3-5 withdrawal fee. Tips are mandatory: 15-20% in restaurants, $1-2 per bag at hotels, 15% for taxi/Uber, $5-10/night for hotel housekeeping. Electricity and phone. Voltage 110-120V, 60 Hz, plugs type A (two flat pins) and B (grounded) — a European adapter is essential. SIM cards: T-Mobile, Verizon, AT&T sell prepaid from $30/month with unlimited internet. Alternatively eSIM (Airalo, Holafly) — buy online before departure. Climate and time zones. The USA has 6 time zones: Eastern (New York, Miami — UTC-5), Central (Chicago, New Orleans — UTC-6), Mountain (Denver — UTC-7), Pacific (Los Angeles, Seattle — UTC-8), Alaska (UTC-9), Hawaii (UTC-10). Climate ranges from tropical Florida (25°C in winter) to arctic Alaska (-30°C). New York has four seasons, California a Mediterranean climate, Texas a hot continental one. Transportation. Domestic flights are cheap and frequent — six major airlines (Southwest, Delta, United, American, JetBlue, Alaska). A rental car is almost mandatory outside big cities — you need an international or Polish driver's license. Amtrak (rail) connects 500 cities but is slow. Metro systems only in New York, DC, Boston, Chicago, San Francisco. Uber and Lyft in every city. Safety and health. The USA is generally safe, but avoid dangerous neighborhoods after dark (South Side Chicago, Skid Row LA, parts of Detroit and Baltimore). Private medical care is very expensive — a doctor's visit costs $200-500, a hospital day $3,000-10,000. Travel insurance with a minimum $500,000 coverage is A MUST. Emergency number 911 (police, ambulance, fire), 311 (city information). Public holidays. New Year's Day (Jan 1), Martin Luther King Jr. Day (3rd Mon of January), Presidents' Day (3rd Mon of February), Memorial Day (last Mon of May), Independence Day (July 4), Labor Day (1st Mon of September), Thanksgiving (4th Thu of November), Christmas (Dec 25). On these days banks and offices are closed, but museums, shops and restaurants stay open.