알다([al-da/know]) means you have information in your head. In polite speech, say 알아요([a-ra-yo]).
알았어요([a-ra-sseo-yo/knew]) is the polite past form. Example: 답을 알았어요 (I knew the answer).
알아야 해요([a-ra-ya hae-yo/have to know]) means you must have the information. Example: 내일까지 알아야 해요 (I have to know by tomorrow).
알다([al-da/know]) means "to know". It is used when you have information in your head.
1. Daily: “답을 알아요 (da-beul a-ra-yo)”
2. Past: 알았어요([a-ra-sseo-yo/knew]) knew.
3. Duty: 알아야 해요([a-ra-ya hae-yo/have to know]) have to know.
4. Warning: 알지 마세요([al-ji ma-se-yo/don't know]) don't know.
A: Do you know that person?
B: 네, 알아요. B: ne, a-ra-yo.B: Yes, I know.
A: 어디서 알아요? A: eo-di-seo a-ra-yo?A: How do you know?
B: 회사에서 알아요. B: hoe-sa-e-seo a-ra-yo.B: I know from work. - 알다([al-da/know])
A: What did you know?
B: 답을 알았어요. B: da-beul a-ra-sseo-yo.B: I knew the answer.
A: 언제 알았어요? A: eon-je a-ra-sseo-yo?A: When did you know?
B: 어제 알았어요. B: eo-je a-ra-sseo-yo.B: I knew it yesterday. - 알았어요([a-ra-sseo-yo/knew])
A: What do you have to know?
B: 비밀번호를 알아야 해요. B: bi-mil-beon-ho-reul a-ra-ya hae-yo.B: I have to know the password.
A: 왜요? A: wae-yo?A: Why?
B: 로그인해야 해요. B: ro-geu-in-hae-ya hae-yo.B: I have to log in. - 알아야 해요([a-ra-ya hae-yo/have to know])
• 알다([al-da/know]) know
- 알았어요([a-ra-sseo-yo/knew]) knew
- 알고 싶어요([al-go si-peo-yo/want to know]) want to know
- 알아야 해요([a-ra-ya hae-yo/have to know]) have to know
- 알지 마세요([al-ji ma-se-yo/don't know]) don't know