learn the ropes
Of nautical origin. The phrase "he knows the ropes" written on a seaman's discharge meant that he was inexperienced and only familiar with a ship's principal ropes.
1981, Snelling, Charles, Nomenclature of Ships, Naval Sea Systems Command:
- To learn the basics or master introductory knowledge.
- Work slowly and cautiously until you have learned the ropes.
- know the ropes
- show one the ropes
- teach one the ropes