naeil sikdang yeyageun miri hae nohasseoyo.

해 놓았어요 comes from 해 놓다, which literally means to do something and leave it in that completed state.

So in this sentence, 예약은 미리 해 놓았어요 does not just mean I made the reservation. It suggests:

• the reservation was made ahead of time
• it is already taken care of
• the result is still in place now

By contrast, 예약했어요 simply means I made the reservation and does not emphasize the idea of having it prepared and set up in advance.

A natural English feeling is:

• 예약했어요 = I made the reservation
• 예약해 놓았어요 = I’ve already made the reservation and it’s all set

The particle 은 is the topic marker, while 을 is the object marker.

Here, 예약은 means something like:

• as for the reservation
• the reservation, at least
• regarding the reservation

This often adds a slight sense of contrast or topical focus. For example, it can imply something like:

• As for tomorrow’s restaurant reservation, I already made it in advance.

If you said 예약을 미리 해 놓았어요, that would also be grammatical, but it would sound more like a straightforward statement about the object.

So:

• 예약을 = focuses more directly on the object of the verb
• 예약은 = introduces the reservation as the topic, often with a subtle contrastive nuance

미리 means in advance, beforehand, or ahead of time.

In this sentence, it modifies the action 해 놓았어요:

• 미리 해 놓았어요 = did it in advance / got it taken care of beforehand

Its placement before the verb is very natural in Korean, since adverbs usually come before the verb they modify.

For example:

• 미리 준비했어요 = I prepared it in advance
• 미리 전화했어요 = I called ahead
• 미리 예약해 놓았어요 = I made a reservation ahead of time

In this sentence, 내일 식당 예약 is best understood as:

• the restaurant reservation for tomorrow

Korean often stacks nouns and time expressions before the main noun. So:

• 내일 = tomorrow
• 식당 = restaurant
• 예약 = reservation

Together, they form a noun phrase meaning something like tomorrow’s restaurant reservation or the reservation at the restaurant for tomorrow, depending on context.

This kind of compressed noun phrase is very common in Korean. English often needs extra words like for, at, or the to make the relationship clearer.

Yes, the subject is most naturally understood as I, but Korean often leaves the subject out when it is obvious from context.

So:

• 내일 식당 예약은 미리 해 놓았어요. naturally means
• I’ve already made tomorrow’s restaurant reservation in advance.

Depending on context, it could also mean we or another understood subject, but I is the most common default in many situations.

This omission is very normal in Korean. You do not need to state 저는 unless there is a reason to emphasize or contrast the subject.

The past form is used because the action of making the reservation has already been completed.

Even though the restaurant visit is tomorrow, the reservation itself was done before now.

So the timeline is:

• restaurant visit: tomorrow
• making the reservation: already happened

That is why Korean uses the past/perfect-like form here:

• 해 놓았어요 = have done it and left it done / already got it taken care of

This is very similar to English saying:

• I’ve already made the reservation for tomorrow.

Yes. In everyday speech, 해 놓았어요 is very often contracted to 해놨어요.

So these are basically the same in meaning:

• 해 놓았어요
• 해놨어요

The shorter form is very common in conversation.

Similarly:

• 사 놓았어요 → 사놨어요 = bought it and have it ready
• 적어 놓았어요 → 적어놨어요 = wrote it down and left it there

A learner should recognize both forms.

-아/어 놓다 is used when someone does something and the result remains, often for future convenience, preparation, or readiness.

Common nuances include:

• do something in advance
• have something ready
• leave something done
• put something in place for later use

Examples:

• 문을 열어 놓았어요.
  = I left the door open.

• 음식을 만들어 놓았어요.
  = I prepared the food in advance.

• 표를 사 놓았어요.
  = I bought the tickets ahead of time.

In your sentence, the nuance is that the reservation is already arranged and ready.

Yes, they overlap somewhat, but together they sound very natural.

• 미리 explicitly says in advance
• 해 놓았어요 adds the idea that it was done and is now set up / taken care of

So using both gives a strong feeling of preparedness:

• I already took care of the reservation ahead of time.

This is not awkward in Korean. In fact, it is a common way to emphasize that something has already been prepared.

Yes, that is grammatical and natural.

• 내일 식당 예약은 미리 했어요. = I made tomorrow’s restaurant reservation in advance.

But compared with 해 놓았어요, it slightly reduces the sense of it’s all set now.

So the difference is roughly:

• 미리 했어요 = I did it ahead of time
• 미리 해 놓았어요 = I did it ahead of time and it is now taken care of / ready

Both are fine, but 해 놓았어요 is especially good when you want to reassure someone that the task has already been completed.

해 놓았어요 is in the polite informal style, often called -어요/-아요 style.

It is polite and commonly used in everyday conversation.

Related levels:

• 해 놓았어요 = polite everyday speech
• 해 놓았습니다 = more formal, polite, often used in announcements or formal situations
• 해 놨어 = casual speech to friends or younger people

So this sentence is polite and natural for normal conversation.