U.S. Currency: Dollar bills are all green and the same size. Pay attention to which bill you give someone. For reference: there are 100 cents in a dollar; the most commonly seen coins are the "quarter" ($.25), the "dime" ($.10), the "nickel" ($.05) and the "penny" ($.01).
Voltage: Voltage in the US is 110AC so expect a variance in power. Use an adapter if possible.