Cultural Anthropology is the study of culture. Anthropologists have a number of subtle definitions for culture, but it can be defined as the shared knowlege of a group of people used to interpret the world and determine the proper way to behave.
Anthropologists have a number of techniques for studying culture. One of the most important is ethnoscience, the particular science of learning what a group of people know. This is accomplished through ethnographic interviews. To perform one, the anthropologist finds an informant (a member of the culture/subculture/microculture willing to talk) and asks this person a series of questions designed to give first a description of the person's daily interactions within the culture in the informant's own language.
This is done so that the anthropologist can then find out what categorizations and definitions the informant uses, thereby preventing the information gathered being ethnocentric (interpreted in terms of the interviewer's own culture.)
Cultural Anthropology is useful for finding out how and why people do things. Other than being interesting, this allows anthropologists to predict and offer solutions to cross cultural conflict. Cultural Anthropology is good training for social hackers.