Warsaw Chopin Airport, Okęcie (WAW), is the biggest and the closest airport to Warsaw City Centre. You can find direct flights to WAW from most of the main European cities/airlines: Amsterdam, Barcelona, Berlin, Brussels, Frankfurt, Madrid, Paris, Rome, Vienna, etc.
26 min from "Warszawa Centralna" (Warsaw Central) Train Station to Warszawa Lotnisko Chopina (Warsaw Chopin Airport), using the S2 and RL train lines. Check out this link for more options: https://www.wtp.waw.pl/en/public-transport-step-by-step/airports-transport/#chopina
Although an EU member, Poland is not part of the euro-zone. Which means they use their own currency "Zloty". The exchange rate is aprox 4.3 Zloty per Euro.
Technically, most establishments in Poland are required to offer an electronic payment option and you should be able to pay with a credit card in shops, restaurants, bars and taxis. However, if you will use the bus to move around in Warsaw, then you may need to pay in cash to the driver. We recommend having some cash in hand, just in case (50zl should be enough for bus rides).
Public transportation in Warsaw is absolutely safe and reliable. There are many bus lines, trams and 2 lines of underground metro. You can buy tickets in every tram/metro stations. We recommend using Google Maps or "jakdojade" app (more accurate) to navigate the city and to check which is the most convenient transportation method, to get to your desired location. If you prefer to move around by car, you can also use ride apps like Uber, Bolt or FreeNow.
As in most of Europe, July means 100% summer season. However, the weather in Warsaw is a bit more unpredictable than other Western European countries (Spain, Italy, etc.). Temperatures could be as high as 20-33 degrees Celsius on a warm day, and as low as 13-21 degrees Celsius during rainy days. We recommend bringing a light jacket and spring-like clothing, just in case!