There are the past making particles which are "했/었/았/였".^^/ For example, 하다 = to do / 했다 = did 먹다 = to eat / 먹었다 = ate 놀다 = to hang out / 놀았다 = hung out 기다리다 = to wait/ 기다렸다 = waited Your sentence would be "그는 사과를 먹+었+다", and making it more natural, "그는 사과를 먹었어요" as for "He ate an apple" On the other hand, "-고 있다" is used for the present progressive. 하다 / 하고 있다 = BE+doing 먹다 / 먹고 있다 = BE+eating (그는 사과를 먹고 있어요 = He is eating an apple) 놀다 / 놀고 있다 = BE + hanging out 기다리다 / 기다리고 있다 = BE + waiting \^o^/

Hey man, These videos are a bit long, but these will show you how to conjugate verbs in Korean which you have to know to be able to speak in the past tense... http://www.learnkoreanonline.net/how-to-korean/learn-korean-how-to-conjugate-verbs-in-korean.html And then this video will get into the past tense a bit more... http://www.learnkoreanonline.net/how-to-korean/learn-korean-an-intro-to-speaking-in-the-past-tense.html Hope that helps.

This question seems to touch too large areas of the Korean language to be answered in this kind of small Q&A board. In my opinion, it is important to know how a Korean verb forms grammatical relations in a sentence. The verbs consist of two parts, one is a root (stem) and the other is an ending particle. All the grammatical relations are defined by the ending particle’s conjugation and the way to express tenses cannot be an exception either.