American Studies is the academic analysis of the various movements, cultures, and subcultures of North America and (mostly) the United States, both past and present. It is the exploration of all things Americana: revolutions, institutions, transformations, religion, race, gender, sexuality, fine arts, popular culture, baseball, apple pie, artifacts, values, customs, ideals, and everyday experience.
The field of American Studies really emerged toward the end of the Great Depression and, especially, after World War II. At first, it focused on national identity, national character, and on exploring the history of thoroughly American cultural concepts like the frontier, the American dream, and rugged individualism. These days, American Studies departments tend to focus more on race, class, gender, ethnicity, and other multicultural issues.
American Studies is an interdisciplinary field. Translation: if it's your major, you are likely to end up taking courses in a variety of disciplines including (but certainly not limited to) history, English, art history, architecture, social sciences, and geography.
What can you do with a major in American Studies? Just like with any liberal arts major, you can do virtually anything. A major in American Studies will mold you into a skilled cultural critic, and it will enhance your abilities to think, write, speak, and do research - all of which will take you far.