Social schemas are 'scripts' or expectations an individual forms about how things operate within their environment. A schema is a cognitive system which helps us organize and make sense of information. Social schemas are developed by individuals for the people in their social environment. They are adaptive because it helps us have expectations about a situation when some of the information is unknown.
An example would be attending a birthday party with a young relative. The child asks you what is going to happen at the party and you tell them there is going to be food, a cake with candles, gifts, and singing. Although you don't know specifically what is going to happen at this particular birthday party you have formed a social schema about birthday parties that was informed by attending them in the past. You used a social schema to fill in unknown information. Social schemas can also shape perception. If you encounter someone yelling loudly repeatedly it may make you scared unless you are at a sporting event and using social schemas know that this is just a fan cheering for their team.