てあげる, てくれる, てもらう: who helps whom?
Describe actions done for someone’s benefit. Compare the actor’s perspective with the perspective of the person receiving help.
Present an action done for you or your side
友だちが駅まで案内してくれました。 says a friend guided you to the station. てくれる presents the action as a benefit to you or someone on your side.
案内しました simply reports an act of guiding. Adding くれました introduces the beneficiary’s perspective, though it does not itself mean that thanks were spoken.
Put the recipient of help first
私は友だちに駅まで案内してもらいました。 describes the same friend doing the guiding. 私 is now foregrounded as the recipient, and 友だちに identifies the actor.
てもらう does not necessarily mean a request came first. It can present receiving someone’s help without specifying how that help was arranged.
Describe what you do for someone else
私は弟に漢字を教えてあげました。 says you taught your younger brother kanji for his benefit. 私 did the teaching and 弟 received the help.
Saying 教えてあげます directly to someone can sound patronizing. Choose an offer suited to the situation, such as 一緒に確認しましょうか。
Quick check: Who cooked in 私は姉に料理を作ってもらいました?
Show the answer and why
姉, the speaker’s older sister, cooked. 私 received the benefit. てもらいました does not mean that the speaker cooked for someone else.