Basically, Social Constructivists believe that groups construct knowledge together, "creating a small culture of shared artifacts with shared meanings. When one is immersed within a culture of this sort, one is learning all the time about how to be a part of that culture on many levels." To a social constructivist, knowledge is a social activity.
Language is probably one of the most obvious examples. We are not born thinking in terms of language but are raised into that culture. Your language and culture determines a large part of who you are, where you get your sense of identity and what your social expectations are. Another example of knowledge being something that is socially constructed is wikipedia.
Watch this short video to learn more.
