biga waseo tteokbokkireul baedalhae dallago haesseo.

Here, 비가 와서 means because it was raining or since it was raining.

Breakdown:

• 비가 오다 = to rain
  
  • literally, rain comes
• 와서 = 오다
  • -아서/어서

The ending -아서/어서 often connects two clauses and can mean:

• and then
• because / so

In this sentence, it is understood as because, so the idea is:

It was raining, so...

That is just the standard Korean expression for weather.

Some common patterns are:

• 비가 오다 = it rains
• 눈이 오다 = it snows

So Korean does not usually say something equivalent to rain falls in the everyday basic form. Instead, it uses 비가 오다, literally rain comes.

Also notice the particle:

• 비가 uses -가, because 비 is the subject of 오다

A natural breakdown is:

• 떡볶이를 = tteokbokki + object marker
• 배달해 = deliver
• 달라고 = saying please do it for me
• 했어 = said / asked

So:

배달해 달라고 했어
= I asked them to deliver it for me

A fuller literal structure is:

• 배달해 달라 = please deliver it for me
• 배달해 달라고 했어 = I said/asked, please deliver it for me

This is a very common reported-request pattern in Korean.

-아/어 달라고 하다 means to ask someone to do something for the speaker.

In this sentence:

• 배달해 달라고 했어 = I asked them to deliver it for me

Compare:

• 해 달라고 하다 = ask someone to do it for me
• 해 주라고 하다 = tell/ask someone to do it for someone else, or with a different perspective

So 달라고 is tied to the speaker’s point of view: do it for me.

Because this sentence is reporting a request, not making the request directly.

Compare these:

• Direct request: 떡볶이 배달해 주세요
  • Please deliver tteokbokki
• Reported request: 떡볶이를 배달해 달라고 했어
  • I asked them to deliver tteokbokki

So:

• 주세요 = what you say directly to someone
• 달라고 했어 = what you use when telling someone later what you asked

Because 떡볶이 is the thing being requested for delivery, so it functions as the object.

In other words:

• What did I ask them to deliver?
• 떡볶이

That is why 떡볶이를 is natural here.

English often handles this with word order alone, but Korean marks the role more explicitly with particles.

Korean often leaves out people or things that are understood from context.

So in:

• 비가 와서 떡볶이를 배달해 달라고 했어

the person or business being asked is omitted. It could be:

• the restaurant
• the store
• the staff
• a delivery person
• someone else nearby

English often wants an explicit object like I asked the restaurant, but Korean can leave that unsaid if it is obvious.

Grammatically, -아서/어서 can sometimes mean either:

• and then
• because

But in this sentence, because is the natural reading:

• 비가 와서 = because it was raining

The logic is:

• It was raining
• So I asked for delivery

If you translated it as it rained and then I asked, it would sound less natural in this context.

This is a very common thing that confuses English speakers.

In Korean, the first clause in a connected sentence does not always need its own past marking if the time is already clear from context or from the main verb.

So:

• 비가 와서 ... 했어 can naturally mean
• It was raining, so I asked...

Korean does not always mirror English tense marking clause by clause.

Also:

• 비가 와서 often suggests the rain was the situation at that time
• 비가 왔어서 can sound more like because it had rained or because it rained earlier, depending on context

So 와서 is very natural here.

했어 is informal, plain spoken style.

Speech-level comparison:

• 했어 = casual informal
• 했어요 = polite
• 했습니다 = formal

So this sentence sounds like something you would say to:

• a friend
• a sibling
• someone younger
• someone you are close to

A polite version would be:

비가 와서 떡볶이를 배달해 달라고 했어요.

Yes. The sentence suggests a very natural real-life situation:

• It was raining
• So the speaker probably did not want to go out
• Therefore, they asked for tteokbokki to be delivered

That extra meaning is not directly stated, but it is strongly implied by the context.

So the sentence is not only about grammar; it also reflects a common Korean everyday situation where delivery food is ordered because of the weather.