The concept of function in functionalist analysis refers to the contribution of the part to the whole. More specifically, the function of any part of society is the contribution it makes to meeting the functional prerequisites of the social system. Parts of society are functional in so far as they maintain the, system and contribute to its survival.
Thus a function of the family is to ensure the continuity by reproducing and socializing new members. A function of religion is to integrate the social system by reinforcing common values.