Complex sentence: Genetic sex determines whether the gonads will be testes or ovaries in the developing embryo if you testes developed it will produce and secrete male sex hormones during late embryonic in early fetal development and caused the secondary sex organs of the male to develop.
Split into simpler sentences: Genetic sex determines whether the gonads will be testes or ovaries. In the developing embryo if your testes are developed it will produce and secrete male sex hormones during late embryonic development and cause the secondary sex organs of the male to develop.