When you are formally introduced to a Spaniard, you should say 'good day' (buenos días señor/señora/señorita) or 'good afternoon/evening' (buenas tardes) and shake hands. Spanish men shake hands on meeting and again on departing, whether it's a casual meeting in the street or a formal occasion. Mature women should be addressed as señora.
'Good afternoon' (buenas tardes) is used instead of 'good day' (buenos días) after lunch, which can start as late as 3 p.m. until 9 or 10 p.m. Good night (buenas noches) is usually used when going to bed or leaving a house late at night.
Another cultural contrast to the U.S. is found in tipping: In Europe, the service charge is included in your bill. As a result, Spaniards only leave propina (tip) if they wish to reward particularly extraordinary service, usually not more than a few coins. Tips are not given for drinks in bars or nightclubs.