First things first: The world-famous American “How are you?” is not so much a question as it is a casual greeting. While “I’m fine, thanks” is a perfectly acceptable answer, going into a 5-minute monologue about how your day has been going so far is not.
That being said, Americans are, on the whole, very friendly people and happy to help when asked. (Southerners have a well-earned reputation as the most hospitable people in the country, and will often go out of their way to make a foreigner feel more at home.) They also tend to be very direct and open, which can come as a surprise to people coming from more reticent cultures.
Outside of a few big cities, most Americans will only speak English, which means it’ll be tough to communicate through a language barrier—although most Americans will gladly try to help as best they can even if they can’t understand you. Americans are also a bit louder and more chatty than the average person, which can make for some energetic interactions.