이해하다([i-hae-ha-da/understand]) means the meaning becomes clear in your head. In polite speech, say 이해해요([i-hae-hae-yo]).
이해했어요([i-hae-hae-sseo-yo/understood]) is the polite past form. Example: 네, 이해했어요 (Yes, I understood).
이해해야 해요([i-hae-hae-ya hae-yo/have to understand]) means the meaning must become clear. Example: 이걸 이해해야 해요 (I have to understand this).
이해하다([i-hae-ha-da/understand]) means "to understand". It is used when meaning becomes clear in your head.
1. Daily: “이해해요? (i-hae-hae-yo)”
2. Past: 이해했어요([i-hae-hae-sseo-yo/understood]) understood.
3. Duty: 이해해야 해요([i-hae-hae-ya hae-yo/have to understand]) have to understand.
4. Warning: 이해하지 마세요([i-hae-ha-ji ma-se-yo/don't understand]) don't understand.
A: Do you understand what it means?
B: 네, 다 이해해요. B: ne, da i-hae-hae-yo.B: Yes, I understand all.
A: 정말 이해해요? A: jeong-mal i-hae-hae-yo?A: Do you really understand?
B: 네, 이해해요. B: ne, i-hae-hae-yo.B: Yes, I understand. - 이해하다([i-hae-ha-da/understand])
A: When did you understand?
B: 방금 이해했어요. B: bang-geum i-hae-hae-sseo-yo.B: I just understood.
A: 어떻게 이해했어요? A: eo-tteo-ke i-hae-hae-sseo-yo?A: How did you understand?
B: 설명을 듣고 이해했어요. B: seol-myeong-eul deu-ko i-hae-hae-sseo-yo.B: I listened to the explanation and understood. - 이해했어요([i-hae-hae-sseo-yo/understood])
A: What do you have to understand?
B: 이걸 이해해야 해요. B: i-geol i-hae-hae-ya hae-yo.B: I have to understand this.
A: 왜요? A: wae-yo?A: Why?
B: 시험이 있어서요. B: si-heo-mi i-sseo-seo-yo.B: Because there's a test. - 이해해야 해요([i-hae-hae-ya hae-yo/have to understand])
• 이해하다([i-hae-ha-da/understand]) understand
- 이해했어요([i-hae-hae-sseo-yo/understood]) understood
- 이해하고 싶어요([i-hae-ha-go si-peo-yo/want to understand]) want to understand
- 이해해야 해요([i-hae-hae-ya hae-yo/have to understand]) have to understand
- 이해하지 마세요([i-hae-ha-ji ma-se-yo/don't understand]) don't understand