The past tense form of adjectives and verbs is formed by adding -았/었 to their word stems.
When the word stem ends in the vowel ㅏ or ㅗ, 았어요 is added.
When it ends in any other vowel, -었어요 is added.
For verbs and adjectives ending in 하다, -였어요 is added to form 히 + 였어요, which is then shortened to 했어요. In the case of the formal polite style, -았/었습니다 and 했습니다 are used.
Details
이다: To be
아니다: Be not
For ex:
Note:While the past tense of 주다 can be written either as 주었어요 or 웠어요，and the past tense of 보다 can be written either as 보았어요 or 봤어요, the past tense of 오다 is written only as 왔어요, not 오았어요.
주다 + -었어요 ᅳ>주었어요 ✓ 줬어요 ✓
보다 + -았어요 一> 보았어요 ✓ 봤어요 ✓
오다 + -았어요 一> 왔어요 ✓ 오았어요 ✕
Kimchi Reader
Indicate that an event happened in the past.
Examples
어제 배가 <span class='focus'>아팠어요</span>. 그래서 잠을 못 <span class='focus'>잤어요</span>.
My stomach hurt yesterday. So I couldn't sleep.
어제 회사 동료하고 저녁을 <span class='focus'>먹었어요</span>.
I had dinner with my colleague yesterday.
남자 친구를 처음 <span class='focus'>만났을</span> 때 첫인상이 <span class='focus'>어땠어요</span>?
What was your first impression when you first met your boyfriend?