i bogoseoneun oneul ane inswaehaeya haeseo peurinteoreul meonjeo kyeosseo.

는 is the topic marker. In 이 보고서는, the speaker is setting this report as the topic of the sentence.

So the feeling is something like:

• As for this report, I turned on the printer first because it has to be printed by today.

Using 는 can also create a slight sense of contrast, depending on context. For example, it can imply this report is the important one right now, maybe compared with other tasks.

If you used 이 보고서가, it would focus more on this report as the subject in a neutral or identifying way.
If you used 이 보고서를, it would make this report the direct object, which does not fit the structure here.

오늘 안에 means by today or within today.

Breakdown:

• 오늘 = today
• 안에 = within, inside the limits of

So 오늘 안에 인쇄해야 해 means:

• I have to print it by today
• literally, I have to print it within today

It emphasizes a deadline that must be met before the day ends.

인쇄해야 해 means have to print or must print.

Breakdown:

• 인쇄하다 = to print
• -아/어야 하다 = have to / must

Since 인쇄하다 ends in 하다, it becomes:

• 인쇄해야 하다

In casual speech, 하다 often becomes 해, so:

• 인쇄해야 해

This is a very common way to express obligation in Korean.

-아서/어서 connects clauses. Here, 해서 means because, so, or since.

So:

• 인쇄해야 해 = I have to print it
• 인쇄해야 해서 = because I have to print it / since I have to print it

The first clause explains the reason for the second clause:

• I had to print this report by today, so I turned on the printer first.

In this sentence, 해서 gives the reason for turning on the printer.

Not always. -아서/어서 can connect two actions in a few ways, often depending on context.

Common uses include:

1. Reason/cause

   • 배가 아파서 병원에 갔어.
   • I went to the hospital because my stomach hurt.

2. Sequence of actions

   • 집에 가서 밥 먹었어.
   • I went home and ate.

In your sentence, it clearly expresses reason:

• 인쇄해야 해서 프린터를 먼저 켰어.
• Because I had to print it, I turned on the printer first.

Korean often leaves out subjects when they are obvious from context.

In this sentence, the omitted subject is most naturally I:

• (나는) 이 보고서는 오늘 안에 인쇄해야 해서 프린터를 먼저 켰어.

But Korean usually does not say 나는 unless it is needed for emphasis or contrast.

This is very normal. In conversation, Korean speakers regularly omit:

• subject
• object
• sometimes other information

as long as the listener can understand it from context.

프린터를 has the object marker 를 because 프린터 is the direct object of 켰어.

• 켜다 = to turn on
• what did the speaker turn on?
• the printer

So:

• 프린터를 켰어 = turned on the printer

The printer is the thing directly affected by the action, so it takes 를.

먼저 means first or before anything else.

So:

• 프린터를 켰어 = I turned on the printer.
• 프린터를 먼저 켰어 = I turned on the printer first.

It suggests that turning on the printer was the first step, probably before doing other things related to printing the report.

This matches real-life logic: you turn on the printer first, then prepare the document, then print it.

켰어 is the correct contracted form of 켜다 in the past casual style.

Breakdown:

• dictionary form: 켜다 = to turn on
• past form: 켜었어 in theory
• but Korean contracts this naturally to 켰어

This kind of contraction is very common.

So:

• 켜다 → 켜요 / 켰어 / 켰어요

not usually:

• 켜어요
• 켜었어

Because the sentence contains two different time meanings:

1. 인쇄해야 해서 = there is a current obligation or deadline

   • it has to be printed by today

2. 켰어 = a completed past action

   • I turned on the printer

So the overall meaning is:

• Because it needed to be printed by today, I turned on the printer first.

The obligation is still relevant, but the action of turning on the printer already happened.

켰어 is casual, informal speech, often called 반말.

Compare:

• 켰어 = casual
• 켰어요 = polite
• 켰습니다 = formal

So this sentence sounds like something you would say:

• to a friend
• to someone younger
• in a casual internal monologue
• in relaxed conversation

If you wanted a polite version, you could say:

• 이 보고서는 오늘 안에 인쇄해야 해서 프린터를 먼저 켰어요.

Yes, in many cases 오늘까지 could be used, but the nuance is slightly different.

• 오늘 안에 = within today, before the day is over
• 오늘까지 = by today, up until today

In this sentence, 오늘 안에 feels very natural because it emphasizes finishing the printing sometime before the end of today.

So:

• 오늘 안에 인쇄해야 해 = I have to print it sometime within today.
• 오늘까지 인쇄해야 해 = I have to print it by today / no later than today.

The difference is small, but 오늘 안에 often feels a little more tied to the idea of completing something during the span of today itself.

Yes. 인쇄하다 is a standard word meaning to print.

It is often used for printing documents, reports, papers, and other physical copies.

You may also hear 출력하다, especially in office or computer contexts. That can also mean to print out. But 인쇄하다 is very common and clear.

So in this sentence:

• 인쇄해야 해 = have to print it

is perfectly natural for printing the report.