"고" or "고나서 is used to conjugate two verbs. Eg: 한국어를 공부하고 영어를 가르칩니다. 세수하고나서 이를 닦습니다. Hope it clear to u now

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 ^^