좋아했어요 - past 좋아했었어요 - further past than 좋아해요 I guess similar with 'had liked'? 했어요 - past 했었어요 - further past than 했었어요 similar with 'had did' so when you want to stress that you did something in the past we use -었어 했어 -> 했었어 -> 했었었어-> 했었었었어 (no further -었어than this, the longer the more exaggerated) I think 했었었어 is not formal(not sure) and 했었었었어 is even more(for 100% sure). I use 했었었어 sometimes even now but 했었었었어 not anymore, people will use that when they are in middle school. Once someone is saying that word, friends were laughing and repeating the words etc etc....

Matthew's explanation is completely correct.

Oh, I saw the correction on your "Why I'm learning Korean" journal that used 았/었/였었 and I wanted to comment on that (writing a lot on my phone is tedious though). I don't see that form used very often, but the other commented is correct and I do think it's similar to "used to V, had Ved, had been Ving". That type of thing. Read over some more example sentences. Input input input (:

I think I got it. Thank you for explaining^^

I'm not Korean, so I didn't put my answer down below, but "었었어요" = past perfect tense = it is difficult to just explain so here are some examples: 먹다 - to eat "In Korea i ate lots of kimchi" = 한국에서 많이 김치를 먹었었어요. Literally it means, when I was in Korea (but now i'm not in Korea) i ate lots of Kimchi. 자다 - To sleep "I used to sleep alone" = 혼자가 잤었어요. = Literally, i used to sleep alone (but now I'm married, OR now i sleep with my dog - I am no longer sleeping alone because....) It is like when one action completely stops, and you will not do it again. 잤어요 = I slept = , so 잤어요 = means i slept, but the action may/ or will continue some other time. Kind of like saying in English = I exercised today었다. I exercised on the weekend for the last time.었었다. In English we just add words to modify the sentence, in Korean the verbs are incredibly specific. I hope this helps, and i apologize for any confusion or errors.