授受表現N4
〜てやる
to do... for (someone/animal)
Structure
V-て形 + やる
Explanation
Verb te-form + やる means doing something for juniors, animals or very close people. Casual; never used toward superiors. E.g., 弟の宿題を見てやる.
Examples
弟に自転車の乗り方を教えてやりました。
I taught my little brother how to ride a bike.
猫にミルクを買ってやります。
I'll buy milk for the cat.
Note
てやる implies doing a favor; use it only with juniors or very close people. For superiors use 〜てさしあげる or 〜てあげる.