Secondary socialization is what occurs when someone leaves their circle of initial socialization, like their family, home and church, and become a part of a larger circle of people that require new rules and types of interaction. When a person goes from their initial circle to their secondary one, there are new rules to learn and new expectations, which can be influenced by or have an influence on initial socialization skills.
Secondary socialization can start at a very young age, like when a child leaves home and starts school for the first time. It can also happen when an adult enters a new organization, like the military or a new religion. In both cases, the child or adult are picking up a new set of social skills, rules and expectations to follow.