教えてあげよう

I'll teach you

→ 教える
phrase Rare #32,159
I'll teach you A volitional form meaning “I’ll teach/tell you” or “let me teach/tell you.” The あげよう implies doing this as a favor for the listener and can sound patronizing depending on context.
JA: このゲームの遊び方を教えてあげよう。
EN: I'll teach you how to play this game.

魚の捕まえ方を教えてあげよう

I’ll teach you how to catch fish.

会合何を言ったらよいか彼女に教えてあげよう

I'll tell her what she should say at the meeting.

教えてあげよう

I'll tell you.

— バジュランギおじさんと、小さな迷子 (2015)

君に自動車の運転法を教えてあげよう

I’ll teach you how to drive a car.