Why boys and girls are different from each other?
There are observable physical differences between a boy and a girl. The boy might have short hair and the girl might have long hair, boys can wear short dress, while some girls refrain from wearing short dresses. These are some of the practices that as a society we have been following and there is no valid reason as to why we are practicing it. In fact, it is better that both boys and girls wear dresses that covers themselves so as to protect themselves from the dust and infections.
Also, there are differences between a boy and girl in terms of their morphology. The boys have penis with two testicles and the girls have vagina and a uterus. The reason for the difference is to enable girls to carry the baby inside the uterus, when they grow up and get married.
Otherwise, in terms of intelligence, physical activities, etc, both boys and girls have similar abilities, except that the interest matters. A boy may be interested in an indoor activity like Chess, while a girl may be interested in playing cricket or hockey. Both are capable of playing the games; but their interest differs.