1Used to agree with what someone said or to answer a question affirmatively — equivalent to English 'yes'.
「明日、来られますか」「はい、行きます」
"Can you come tomorrow?" "Yes, I'll be there."
店員に「お持ち帰りですか」と聞かれ、「はい」と答えた。
The clerk asked, "Is this to go?" and I answered, "Yes."
「これで間違いないですね」「はい、間違いありません」
"This is correct, right?" "Yes, it's correct."
全員が賛成し、「はい」と声を揃えて答えた。
Everyone agreed and answered "yes" in unison.
2A response showing you've understood an instruction or explanation — meaning 'understood', 'I see', or 'OK'.
「この資料を3時までにお願いします」「はい、承知しました」
"Please have this document ready by 3 o'clock." "Understood, I'll take care of it."
先生に注意されて、「はい」とうなずいた。
The teacher warned me, and I nodded, saying "OK."
「危ないから触らないで」「はい」
"Don't touch it, it's dangerous." "OK."
3A response to roll call, indicating that you are present when your name is called.
先生が名前を呼ぶと、生徒たちは次々に「はい」と答えた。
As the teacher called out names, the students answered "here" one after another.
名前を呼ばれた田中さんは、大きな声で「はい」と返事した。
When Tanaka's name was called, he answered "present" in a loud voice.
4Used with rising intonation to ask someone to repeat themselves when you didn't catch what they said.
「田中さん、ちょっといい？」「はい？」
"Tanaka, got a minute?" "Huh?"
声が小さくて聞き取れず、「はい？もう一度お願いします」と言った。
I couldn't hear because the voice was too quiet, so I said, "Sorry? Could you say that again?"
5Used when handing something over or calling for someone's attention, similar to 'here' or 'here you go'.
店員が商品を渡しながら「はい、どうぞ」と言った。
The clerk handed over the item, saying, "Here you go."
「はい、次の人」と言って、係員が列を進めた。
"Next, please," said the staff member, moving the line along.
6An uncommon usage as a cue shouted to urge a horse or animal forward, like 'giddy-up'.
馭者は馬に「はいっ」と声をかけて歩き出させた。
The driver shouted "giddy-up" to the horse and got it moving.