Americans seldom speak languages other than English, unless they are from an immigrant community; visitors are generally expected to speak and understand English. Documentation on sights etc. is generally only available in English, though some sites have documentation in Chinese, French, German, Japanese etc. Product labels may be translated into French (because the same product is sold in Québec) and Spanish, though some of these translations are badly done.
The majority of American accents are derived from Irish and British accents, with some Dutch influence. There are fascinating regional accents in the South and Texas, in New England, in New York City, and in the upper Midwest, but aside from pronunciation and a few colorful local phrases Americans from different regions mostly speak English. Americans tend to speak their native dialect, but when speaking formally, they may switch to something similar to a flat "Midwestern" accent, much popularized by radio, TV and movies. Many will also try to speak this way if they realize you have trouble understanding them. However, people with strong local accents may be difficult for non-native English speakers to understand.
Many African Americans, and some Americans of other ancestries, speak what linguists refer to as "African American Vernacular English", commonly referred to as "ebonics". AAVE is related to the nation's southern varieties of English, but some linguists suggest it also retains elements of grammar from the Bantu and Niger-Congo language families.
In many parts of the U.S., such as California, the Southwest, Texas, Florida, Illinois, and New York, Spanish is the first language of a large minority of residents, mostly immigrants from Mexico or Latin America. Although it's rare to be in areas where no one speaks English, a good handle on Spanish can make communications easier in some areas. In addition to English and Spanish, French is spoken in rural areas near the border with Quebec and by immigrants from West Africa and Haiti, Hawaiian is the native language of Hawaii and in the various Chinatowns in the US's major cities, Chinese is common. Smaller immigrant groups also sometimes form their own pockets of shared language, including Russian, Italian, Greek, Arabic, Tagalog, and Vietnamese. Another pocket comprises a group that has been in the country for generations, the Amish, who live in Pennsylvania and Ohio and speak a variety of German, and some Native Americans speak their respective native languages, especially on reservations in the west.
Compared to some western countries, Americans tend to be very politically natured. It may be surprising to some that many radio and TV stations spend most of the day broadcasting political talk shows. Some Americans may have strong feelings about local politics and US foreign policy, and it is wise to be courteous when talking about politics in general with Americans. Usually they will extend the same courtesy to you.