〜てあげる
do (something) for someone
Verb て-form + あげる
Sign up free to review this point on a spaced schedule.
The giving verbs also attach to the て-form, and then what's given is an action. てあげる is doing something for someone else: 妹に宿題を教えてあげました, "I helped my sister with her homework".
The direction rules are the same as for あげる: from you outward, or between other people.
Be careful with it to someone's face. 手伝ってあげます can sound like "I'll do you the favour of helping". With superiors or people you don't know well, just offer the action: 手伝いましょうか, "shall I help?"
Among friends and family it's perfectly natural, and very common when talking about what you did for others.
Examples
妹に宿題を教えてあげました。
I helped my little sister with her homework.
友達を駅まで送ってあげた。
I gave my friend a lift to the station.
おばあさんの荷物を持ってあげました。
I carried an old lady's bags for her.
毎晩、子どもに本を読んであげます。
I read to my child every night.
写真を撮ってあげようか。
Want me to take a photo for you?