know the ropes
Be informed about the details of a situation or task. For example, Don't worry about Sara's taking over that reporter's jobshe already knows the ropes. This expression alludes to sailors learning the rigging so as to handle a sailing vessel's ropes. It was being used figuratively by the late 1800s. The same allusion is present in show someone the ropes, meaning "to familiarize someone with the details," as in Tom's very experiencedhe'll show you the ropes.