Direction/Means

(으)로: the particle that does six different jobs

If you only learn one thing about (으)로, make it this: it's less a single particle than a hinge. It shows up everywhere, and the meaning changes with the verb sitting next to it.

Which form to attach

• 로 after a vowel: 학교로 (hakgyo-ro), "to school"
• 로 after ㄹ as well: 지하철로 (jihacheol-ro), "by subway"
• 으로 after every other consonant: 손으로 (son-euro), "with the hand"

That ㄹ exception is the one people forget. 지하철 ends in a consonant, but because it's ㄹ it still takes plain 로.

Direction: "toward"

• 어디로 가요? (eodi-ro gayo?) — "Where are you headed?"
• 오른쪽으로 도세요. (oreunjjog-euro doseyo) — "Turn right."

에 vs 로, which is the real question

Both can follow a place before a movement verb, and this is where learners stall. The difference is arrival versus heading.

• 학교에 가요. (hakgyo-e gayo) — "I'm going to school." The school is the destination; you end up there.
• 학교로 가요. (hakgyo-ro gayo) — "I'm heading toward school." The emphasis is the direction you're taking.

In everyday speech they overlap a lot and nobody will misunderstand you. But 로 is the one you want when the point is which way, which is why direction questions and turn-by-turn instructions use it.

Means and instrument: "with, by"

• 젓가락으로 먹어요. (jeotgarag-euro meogeoyo) — "I eat with chopsticks."
• 버스로 왔어요. (beoseu-ro wasseoyo) — "I came by bus."
• 한국어로 말해요. (hangugeo-ro malhaeyo) — "I speak in Korean."

Language names take 로 too, which surprises people. "In Korean" is 한국어로, not 한국어에서.

Material: "made of"

• 나무로 만들었어요. (namu-ro mandeureosseoyo) — "It's made of wood."

Change: "into"

• 물이 얼음으로 변했어요. (mur-i eoreum-euro byeonhaesseoyo) — "The water turned into ice."
• 원을 달러로 바꿨어요. (won-eul dalleo-ro bakkwosseoyo) — "I changed won into dollars."

Cause: "because of"

• 감기로 결석했어요. (gamgi-ro gyeolseokaesseoyo) — "I was absent because of a cold."

This one is formal and shows up in writing and announcements far more than in conversation, where 때문에 does the job instead.

Why the list doesn't need memorizing

Six meanings sounds like six things to learn, and it isn't. The thread running through all of them is the route something takes — through space, through an instrument, through a material, through a change of state. Once you see 로 as "by way of", the senses stop feeling unrelated.