Sociology is a field of study that attempts to explain how society and the groups a person belongs to affect the ways in which people behave. This is as opposed to psychology, for example, which looks at people simply as individuals.
A functionalist looks at various parts of society as parts of a body. It argues that all the parts of a society get to be that way because they serve an important function.
A conflict perspective says societal institutions get to be that way by conflict -- they are basically imposed by the elites through conflict.
Interactionists are more like psychologists, saying that society is made up of the interactions of individuals.