1To give something to the speaker or someone in the speaker's in-group. The direction of giving is built into the verb — toward the speaker's side — which is what distinguishes it from あげる (speaker → other). Almost always written in kana; the kanji 呉れる is rarely seen.
友達が誕生日に本をくれた。
A friend gave me a book for my birthday.
上司が出張のお土産をくれた。
My boss gave me a souvenir from his business trip.
妹は私にチョコレートをくれた。
My little sister gave me some chocolate.
これ、本当にくれるの？ありがとう！
You're really giving me this? Thank you!
2Usually in the form くれてやる — a rough, brusque way of saying "I'll give it to you," with a tone of disdain or contempt toward the receiver. Heard in quarrels or defiant utterances rather than neutral speech.
そんなに欲しいなら、くれてやるよ。
If you want it that badly, fine — take it.
こんな金、お前にくれてやる。
Money like this? I'll just toss it your way.
3Auxiliary after a verb's -te form, in the pattern 〜てくれる: it marks that someone does an action for the benefit of the speaker (or the speaker's in-group). A core piece of Japanese giving/receiving grammar, used for thanks and requests alike (〜てくれる？ / 〜てくれませんか). Compare 〜てもらう (receiver is subject) vs. 〜てくれる (giver is subject).
手伝ってくれてありがとう。
Thanks for helping me out.
友達が駅まで車で送ってくれた。
My friend drove me to the station.
雨が降ってきたので、彼が傘を貸してくれた。
It started raining, so he lent me an umbrella.
ちょっと待っててくれる？
Could you wait a moment for me?
母はいつも私の話を聞いてくれる。
My mother always listens to what I have to say.
4An ironic use of 〜てくれる that blames or sarcastically complains about an action whose result was inconvenient or harmful to the speaker. Typically takes the past form plus the sentence-final particle な or ね — 〜してくれたな, 〜してくれたね — literally "how kind of you to ___" but meaning the opposite.
余計なことを言ってくれたな。
Thanks a lot for saying something you didn't need to.
せっかくの計画を台無しにしてくれたね。
Well, you really managed to ruin the plan we'd put together.
彼は土壇場でドタキャンしてくれた。
He went and cancelled on me at the last possible minute.