In some places, boys and girls are often separated when they play or study. This is called sex segregation. One reason for this is that people believe it's better for boys and girls to learn and grow up in separate environments. In Islam, some people believe that this is a good way to protect the modesty and purity of both boys and girls, so they separate them in school, public places, and sometimes even in their homes.
This does not mean that boys and girls do not interact or communicate with each other. They still do, but they are generally kept in separate groups or areas. For example, they may have separate gym classes, or girls may sit on one side of the classroom and boys on the other.
It's important to note that not all followers of Islam believe in sex segregation, and even those who do may practice it differently depending on their culture, interpretation of religious texts, and personal beliefs.