biga waseo chinguege usaneul billyeo jwosseoyo.

Here, -아서/어서 means because.

So 비가 와서 means because it was raining or since it was raining.

A useful thing to know is that -아서/어서 can also connect two actions in a sequence, like and then. But in this sentence, the most natural reading is reason/cause:

• 비가 와서 → because it was raining
• 친구에게 우산을 빌려 줬어요 → I lent my friend an umbrella

So together, it means something like Because it was raining, I lent my friend an umbrella.

Because 오다 changes when you add -아서.

• dictionary form: 오다 = to come
• stem: 오-
• 오 + 아서 contracts to 와서

So:

• 오아서 → not used
• 와서 → correct

This is a very common contraction:

• 오다 → 와요
• 오다 → 와서
• 오다 → 왔어요

가 is the subject marker, and in weather expressions it is very common.

• 비가 오다 = rain comes / it rains

So 비가 와서 is the normal way to say because it was raining.

If you said 비는 와서, it would sound more contrastive, as if you were emphasizing as for the rain... or contrasting rain with something else. In a plain, neutral sentence, 비가 와서 is the natural choice.

에게 marks the person who receives something or is affected as the target of the action.

Here:

• 친구에게 = to my friend

So:

• 친구에게 우산을 빌려 줬어요 = I lent an umbrella to my friend

You can think of 에게 here as similar to to in English.

Also, in everyday speech, 친구한테 is very common and means basically the same thing:

• 친구에게 우산을 빌려 줬어요
• 친구한테 우산을 빌려 줬어요

Both are natural.

This is one of the most common points of confusion.

By itself:

• 빌리다 = to borrow

But when you use 빌려 주다, it means:

• to let someone borrow
• in natural English, to lend

So:

• 우산을 빌렸어요 = I borrowed an umbrella
• 우산을 빌려 줬어요 = I lent someone an umbrella

The 주다 adds the idea of doing the action for someone / giving the benefit to someone. In this case, that becomes lending.

주다 literally means to give, but after another verb it often means to do something for someone.

So:

• 빌리다 = to borrow
• 빌려 주다 = to let someone borrow, literally something like to borrow-and-give

In natural English, we usually translate that as to lend.

This pattern appears with many verbs:

• 사 주다 = to buy for someone
• 가르쳐 주다 = to teach someone / show someone
• 도와주다 = to help

So in your sentence, 주다 shows that the action is done for the friend’s benefit.

줬어요 is the polite past form of 주다.

It comes from:

• 주다
• 주었어요
• contracted to 줬어요

So 빌려 줬어요 is the polite past form meaning lent or gave to borrow.

A similar pattern happens often in Korean:

• 보다 → 보았어요 → 봤어요
• 주다 → 주었어요 → 줬어요

Korean often leaves out the subject when it is obvious from context.

So even though there is no explicit I, the sentence naturally means:

• I lent my friend an umbrella

If you wanted to include the subject, you could say:

• 제가 비가 와서 친구에게 우산을 빌려 줬어요.

But in normal conversation, leaving it out is very common and sounds natural.

Korean often omits possessive words like my, your, or his/her when the meaning is clear from context.

So 우산을 빌려 줬어요 can naturally mean:

• I lent my umbrella
• or just I lent an umbrella

Usually, listeners understand that it is probably the speaker’s umbrella unless context suggests otherwise.

If you wanted to make it explicit, you could say:

• 제 우산을 친구에게 빌려 줬어요. = I lent my umbrella to my friend.

But the original sentence is completely natural without 제.

Yes, -아서/어서 can sometimes connect actions as a sequence:

• did A, and then did B

However, in this sentence, the reason reading is much more natural:

• Because it was raining, I lent my friend an umbrella

Why? Because lending someone an umbrella is a very natural response to rain, so the cause-and-effect relationship is obvious.

So while the grammar can sometimes express sequence, here it is best understood as because.

This is a very important contrast.

1. 친구에게 우산을 빌려 줬어요

   • 에게 = to my friend
   • 빌려 주다 = to lend
   • meaning: I lent my friend an umbrella

2. 친구에게서 우산을 빌렸어요

   • 에게서 = from my friend
   • 빌리다 = to borrow
   • meaning: I borrowed an umbrella from my friend

So the key differences are:

• 에게 = to
• 에게서 = from
• 빌려 주다 = lend
• 빌리다 = borrow

This is a pair that many learners mix up at first.

Yes, Korean word order is more flexible than English, as long as the particles show each word’s role.

The original sentence:

• 비가 와서 친구에게 우산을 빌려 줬어요.

You could also say:

• 비가 와서 우산을 친구에게 빌려 줬어요.

Both are understandable because:

• 친구에게 marks the recipient
• 우산을 marks the object

That said, the original order sounds very natural and smooth. In Korean, the verb usually comes at the end, but before that, there is often some flexibility.