riheoseori kkeutnago keoteuneul yeoreosseo.

이 is the subject marker. It shows that 리허설 (rehearsal) is the subject of 끝나고.

So in this sentence:

• 리허설이 끝나고 = the rehearsal ended / after the rehearsal ended

A very literal breakdown is:

• 리허설 = rehearsal
• 이 = subject marker
• 끝나고 = ended and / after ending

Because 끝나다 is an intransitive verb, the thing that ends takes a subject marker like 이/가.

This is a very common question because the two verbs are related but different:

• 끝나다 = to end, to be finished
  
  • something ends by itself
• 끝내다 = to finish something, to bring something to an end
  
  • someone finishes something

Here, the sentence says:

• 리허설이 끝나고 = the rehearsal ended / after the rehearsal ended

So 끝나다 is correct, because the rehearsal is what ended.

Compare:

• 리허설이 끝났어. = The rehearsal ended.
• 우리가 리허설을 끝냈어. = We finished the rehearsal.

So if the rehearsal itself is the subject, use 끝나다.

Here, -고 connects two actions or events.

In this sentence, it gives the sense of:

• and then
• after
• once

So:

• 리허설이 끝나고 커튼을 열었어.

can be understood as:

• The rehearsal ended, and then [someone] opened the curtain.
• After the rehearsal ended, [someone] opened the curtain.

In many situations, -고 simply links events in sequence.

So the structure is:

• 끝나고 = ending, and then... / after ending...
• 열었어 = opened

In Korean, when clauses are connected, the tense is often shown clearly only in the final verb.

So even though 끝나고 does not visibly have past tense marking here, the sentence naturally implies a past sequence because the final verb is past:

• 열었어 = opened

That makes the whole sentence read as a past event:

• The rehearsal ended, and then [someone] opened the curtain.

This is very normal in Korean.

You could sometimes see more explicitly past-looking forms in other structures, but with -고, leaving the first verb as 끝나고 is completely natural.

It can feel like both, depending on context.

In this sentence, -고 strongly suggests sequence:

• first, the rehearsal ended
• then, the curtain was opened

So in English, the best translations are often:

• The rehearsal ended, and then the curtain was opened/opened.
• After the rehearsal ended, [someone] opened the curtain.

If two actions are clearly happening one after another, -고 often has that and then / after feeling, not just a neutral and.

Korean often omits subjects when they are obvious from context.

So 커튼을 열었어 literally means:

• [Someone] opened the curtain.

The subject could be:

• I
• we
• they
• another person already understood from context

That is very normal Korean. You do not need to say the subject every time.

For example:

• 리허설이 끝나고 내가 커튼을 열었어. = After the rehearsal ended, I opened the curtain.
• 리허설이 끝나고 커튼을 열었어. = After the rehearsal ended, [I/we/someone] opened the curtain.

The listener usually figures it out from the situation.

을 is the object marker.

It marks 커튼 (curtain) as the thing being opened.

So:

• 커튼을 열었어
  • 커튼 = curtain
  • 을 = object marker
  • 열었어 = opened

Since 열다 means to open something, it takes an object.

Compare:

• 문을 열었어. = [I] opened the door.
• 창문을 열었어. = [I] opened the window.
• 커튼을 열었어. = [I] opened the curtain.

열었어 is in the casual/plain informal style.

Compare:

• 열었어 = casual, used with friends, younger people, close relationships, or in narration
• 열었어요 = polite
• 열었습니다 = formal

So the same sentence in polite speech would be:

• 리허설이 끝나고 커튼을 열었어요.

The grammar is the same; only the speech level changes.

The dictionary form is 열다, which means to open.

Conjugation:

• 열다 → stem 열-
• past marker -었-
• casual ending -어
• 열었어

So:

• 열다 = to open
• 열었어 = opened

No, 리허설 is a loanword from English rehearsal.

Korean uses many loanwords, especially for performance, music, theater, media, and modern life.

So 리허설 is a very normal Korean word, even though it comes from English.

Yes, 커튼을 열다 is natural.

In Korean, 열다 can be used with things like:

• 문을 열다 = open a door
• 창문을 열다 = open a window
• 커튼을 열다 = open a curtain

For curtains, Korean may also use:

• 커튼을 치다
• 커튼을 걷다
• 커튼을 열다

depending on the exact type of curtain and the action meant. But 커튼을 열었어 is understandable and natural enough, especially in a stage or performance context.

If this is a theater curtain, the sentence may sound like:

• After the rehearsal ended, [we/they] opened the curtain.

Not necessarily.

In Korean, -고 can connect clauses even when the subjects are different, as long as the meaning is clear.

In this sentence:

• 리허설이 끝나고 — subject: 리허설
• 커튼을 열었어 — subject: omitted, but understood from context

So the subjects are actually different already:

• the rehearsal ended
• someone opened the curtain

That is completely normal.

No, that would be incorrect.

You need:

• 리허설이 끝나고

because 끝나다 takes a subject, not an object.

So:

• 리허설이 끝나다 = the rehearsal ends

But if you use 끝내다, then you can use 을:

• 리허설을 끝내고 = after finishing the rehearsal

So these are both possible, but they mean slightly different things:

• 리허설이 끝나고 = after the rehearsal ended
• 리허설을 끝내고 = after finishing the rehearsal

Both can mean roughly the same thing, but the nuance is a little different.

• 리허설이 끝나고 커튼을 열었어

  • more direct
  • natural for narrating events in sequence
  • the rehearsal ended, and then the curtain was opened

• 리허설이 끝난 후에 커튼을 열었어

  • more explicitly after
  • slightly more formal or structured
  • after the rehearsal had ended, the curtain was opened

So -고 is often great for simple event flow, while 후에 makes the time relationship more explicit.

Yes.

Korean often leaves out pronouns like I, we, or they when they are understood from context.

So depending on the situation, this sentence could naturally mean:

• After the rehearsal, I opened the curtain.
• After the rehearsal, we opened the curtain.
• After the rehearsal, they opened the curtain.

The Korean sentence itself does not force a specific subject for 열었어. Context decides it.

The ending -어 in 열었어 is the casual spoken ending.

Different endings give different styles:

• 열었어 = casual spoken
• 열었어요 = polite spoken
• 열었다 = plain written / narrative / dictionary-style declarative tone in some contexts

So this sentence sounds like normal casual conversation or informal storytelling.

If you changed it to 열었다, it would sound more like written narration, diary style, or a blunt/plain statement rather than casual speech.