I found the right answer to this question ^^
I know now how to conjugate a Korean verb in the present and the past tense.
* Present:
There are 3 categories:
1/ If the last vowel is "ㅏ" or " ㅗ" then we add "아요"
가다 = to go ( dictionary form) --> 가 + 아요 = 가요
보다 = to see, to watch, to look --> 보 + 아요 = 봐요
2/ If the last vowel is NOT "ㅏ" or " ㅗ" then we add "어요"
웃다 = to laugh --> 웃 + 어요 = 웃어요
먹다 = to eat --> 먹 + 어요 = 먹어요
3/ If the verb stem is " 하 " then we add " 여요"
하다 = to do --> 하 + 여요 = 하여요 and it became 해요
( Mybe it will be clearer if you know I love you in Korean, it is 사랑해요 and it is:
사랑하다 --> 사랑 + 해요 = 사랑해요 )
* The past: same rules just the endings "아요", "어요" and "여요" became "았어요" , "었어요" and "였어요". So,
1/ 사다 = to buy --> 사 + 았어요 = 샀어요
오다 = to come --> 오 + 았어요 = 왔어요
2/ 적다 = to write down --> 적 + 었어요 = 적었어요
3/ 하다 = to do --> 하 + 였어요 = 했어요
Note: All these verbs are in polite form
Hopefully, it will help you ^^
