Learn Hardcore Korean: nagal ttae keompyuteoreul kkeoyo. - I turn off the computer when I leave.

때 is a bound noun meaning “time/when.”
To say “when [someone] does/will do,” attach the adnominal ending -(으)ㄹ to the verb stem, then add 때: 나가- + ㄹ + 때 → 나갈 때. This points to the time of leaving (future/unrealized relative to the main clause, or a general habitual time).
Forms like 나가는 때 are grammatically possible but are rarely used in this meaning; speakers overwhelmingly prefer 나갈 때.

Could I say 나가면 컴퓨터를 꺼요 instead? What’s the difference?

-(으)면 marks a condition (“if/when”). In many contexts 나가면… overlaps with 나갈 때…, but:
- 나갈 때 focuses on the timing of the action (“at the time of leaving”).
- 나가면 feels more conditional/procedural (“in the case that I go out, I turn it off”), good for rules.

What about 나가기 전에? Is that more natural?

-기 전에 means “before doing.” 나가기 전에 컴퓨터를 꺼요 is very natural and slightly clearer that the turning off happens prior to stepping out.
나갈 때 is also fine and implies “at the time of leaving,” which in practice is just before you go.

Can I use 나가면서 here?

-면서 means “while/as (simultaneous actions).” 나가면서 컴퓨터를 꺼요 sounds odd because you can’t really be walking out and turning off the computer at exactly the same moment.
Use 나갈 때 or 나가기 전에 instead.

Why is it 나가다 and not 나오다?

나가다 = go out (away from the current place).
나오다 = come out (toward the speaker’s position). In general statements/instructions like this, 나가다 is the standard choice.

Do I need to add 밖에 (outside), like 밖에 나갈 때?

Usually no. 나가다 already implies going out. Add 밖에 only if you’re contrasting with going “in” somewhere else or for emphasis.

Why is it 컴퓨터를? Can I drop 를 or use 는?

-를/-을 marks the direct object; the computer is what you’re turning off.
In casual speech the object marker can drop: 컴퓨터(를) 꺼요. Keeping it sounds a bit clearer/more formal.
컴퓨터는 꺼요 makes “computer” a topic/contrast: “As for the computer, I do turn it off (maybe other devices I don’t).”

How does 끄다 → 꺼요 work? Is it irregular?

Base verb: 끄다 (“to turn off”).
With -아요/어요, stem-final ㅡ drops and you add -어/어요: 끄 + 어요 → 꺼요.
Common forms:
- Present (informal polite): 꺼요
- Past: 껐어요
- Formal polite: 끕니다
- Imperative polite: 끄세요

What’s the difference between 컴퓨터를 꺼요 and 컴퓨터가 꺼져요?

컴퓨터를 꺼요: active — “I turn the computer off.”
컴퓨터가 꺼져요: passive/resultative — “The computer goes/gets turned off” (by itself or unspecified agent).
State: 컴퓨터가 꺼져 있어요 = “The computer is (in the state of being) off.”

Why is the subject (“I”) missing? Can I add it?

Korean often omits obvious subjects. Context supplies “I/we.”
You can add it:
- 저는 나갈 때 컴퓨터를 꺼요.
- If the subject of the 때-clause differs, mark it: 민수가 나갈 때 저는 컴퓨터를 꺼요 (“When Minsoo leaves, I turn off the computer.”)

How do I make this an instruction, and how do I add honorifics?

Is the word order flexible? Could I say 컴퓨터를 나갈 때 꺼요?

Most natural: put the time clause first — 나갈 때 컴퓨터를 꺼요.
컴퓨터를 나갈 때 꺼요 is understandable but awkward; keep adverbial -때 clauses before the main clause.

Does 나갈 때 mean “whenever I go out”? How do I say “every time”?

나갈 때 can be generic/habitual or refer to a specific upcoming instance; context decides.
To say “every time,” use -때마다: 나갈 때마다 컴퓨터를 꺼요.
Emphasis/contrast: 나갈 때는 컴퓨터를 꺼요 (“As for when I leave, I turn it off.”)

What about spacing? Is 나갈때 okay?

Write a space before 때: 나갈 때. Writing 나갈때 is incorrect in standard spacing.

How do I pick between 나갈 때, 나갔을 때, and 나가던 때?

나갈 때: time of a future/unrealized or general/habitual action.
나갔을 때: a specific time in the past (“when I went out”).
나가던 때: ongoing/habitual in the past (“when I used to go out / was in the process of going out”).

How do I form -(으)ㄹ 때 with other verbs?