-곤 하다 abbreviated from -고는 하다 A. V. + 곤 하다 => "from time to time, it does," "now and then" A.V. + 곤 했다 => "used to" This pattern indicates a repeated action. It means "from time to time" or "now and then" when it ends in the present tense, and it means "used to" when it ends in the past tense. 캘리포니아에서는 가끔 지진이 나서 사람들을 놀라게 하곤 한다. => From time to time in California, there is an earthquake and it shocks people. 친구가 가끔 들르곤 한다. => My friend stops by now and then. 남들 따라서 외국 풍습에 잘 휩쓸리곤 했다. => I used to follow foreign custom blindly. 밤이면 아기가 울곤 했다. => The baby used to cry at night. 저는 어릴 때 미국에서 축구를 했어요. I played football in America when I was young. 저는 어릴 때 미국에서 축구를 하곤 했어요. I used to play football in America when I was young. This pattern is commonly used in reminiscences.

했다 : I played soccer when i was young. 하곤했다 : I would play soccer when i was young They both can mean i played soccer repeatedly, in my opinion.

했다 = Simple past tense; --> 곤 했다 = Regularly did something in the past. 동사 + 곤 하다; used to say that you did/ do something regularly. Because if you say 축구를 했다 = It can imply that you played it once or a couple of times, but you didn't do it regularly (as a sport or hobby). Hope this helps.

When Korea students learn English, they learn that -하곤했다 can be translated to used to-. For me, I'd rather say 저는 어릴 때 미국에서 축구를 했어요. we don't say -하곤 했다 a lot when we speak.