to be very familiar with something; to have a thorough understanding of something
何かに非常に詳しい; 何かを十分に理解している (nanika ni hijou ni kuwashii; nanika o juubun ni rikai shiteiru)
"He really knows the ropes in this field of work."
"彼はこの仕事の分野で本当に経験豊富だ" (kare wa kono shigoto no bunya de hontou ni keiken houfu da)
