We learned earlier that the verbs, あげる、くれる、and もらう describe transactions of things Here we will learn the use of these words as helping verbs. When these verbs follow the te-form of a verb, they describe the giving and receiving of services.
＜〜てあげる＞
We use te-form + あげる when we do something for the sake of others, or somebody does something for somebody else The addition of the helping verb あげる does not change the basic meaning of the sentences, but puts focus on the fact that the actions were performed “on demand” or “as a favor”.
銀行は、わたしに、お金を貸しました。
The Bank lent me money.
（貸す、のてフォームはなんでしょう？）
わたしはたけし君に、お金を貸してあげました。
I lent Takeshi money. (To help him)
Bank lent you money for their business, so 貸した is fine. However, if you lent your friend money, you are so generous and help your friend. So you say 貸してあげた
However, even some Japanese say あげる incorrectly because sometines they don’t notice that receiver does not appreciate the action. It’s called 押し付けがましい meaning “self assertive”。So for the speaker, it’s correct, though, it’s not correct for receiver.
I taught him what happened at the end of the movie. （教える、のてフォームはなんでしょう？）
わたしは、彼に、映画の結末を教えてあげました。
ネタばらし
Spoiler
Note that all these といい sentences mean that you are hoping that something nice happens. This means that these patterns cannot be used in cases where you hope to do something nice, which is under your control. In such cases, you can usually turn the verb into the potential form.
I bought him a pink Jacket.
わたしは、彼にピンクのジャケットを買ってあげました。
My dad took my brother to the airport.
お父さんは、兄を空港に連れて行ってあげました。
＜〜てくれる＞
Now, let’s learn about くれる
We use くれる when somebody does something for us.
（１）I lent Takeshi money. (To help him)
わたしはたけし君に、お金を貸してあげました。
She lent me money.
彼女は、僕に、お金を貸してくれました。
（２） I help him with his homework.
わたしは、彼に宿題を手伝ってあげました。
She helped me with my homework.
彼女は、僕の宿題を手伝ってくれました。
(3) I bought him a pink Jacket.
わたしは、彼にピンクのジャケットを買ってあげました。
She bought a pink jacket for me.
彼女は、僕にピンクのジャケットを買った。
（４）My dad took my brother to the airport.
お父さんは、兄を空港に連れて行ってあげました。
My dad took me to the airport.
父は、僕を空港に連れて行ってくれました。
＜〜てもらう＞
We use the te-form + もらう to say that we get, persuade, or arrange for, somebody to do something for us. In other words, we “receive” somebody’s favor. The person performing the action for us is accompanied by the particle に。
I got her to help me with my homework.
僕は、彼女に宿題を手伝ってもらいました。(Spot light – me)
Compare the last sentence with the くれる version below. They describe more or less that same event, but the subjects are different. In もらう sentences, the subject is the beneficiary. In くれる sentences, the subject is the benefactor.
She helped me with my homework. (Spot light – her)
彼女は、僕の宿題を手伝ってくれました。
My dad took me to the airport.
父は、僕を空港に連れて行ってくれました。(spot light – my father)
I got my dad to take me to the airport.
僕は、父に空港に連れて行ってもらいました。(spot light – me)
How to use に in this case!
In direct translation, it would be,
“ I was taken to the airport by my dad since the spot light is “me” in this sentence,
So, “By dad” means 父に。
My mom baked the birthday cake since my younger sister asked her. (On demand)
妹が頼んだので、母は、誕生日ケーキを焼いてあげました。
My mom baked the birthday cake. (Spot light- my mom)
母は、誕生日ケーキを焼いてくれました。
My sister got my mom to bake her birthday cake. (Spot light – my sister)
私の妹は、母に、誕生日ケーキを焼いてもらいました。