This is a somewhat confusing conjunction because it doesn't have a good English equivalent. It marks the preceding clause as background information. Here are some examples from Using Korean
저 한국 가는데
뭐 부탁할 거 없어요?
I'm going to Korea; do you have anything to ask of me?
[Here, going to Korea is background information that gives context for the question that's the main point of the sentence.]
부탁드릴 게 한 가지 있는데
좀 들어 주시겠어요?
I have one favor to ask of you; would you do it for me?
어제 백화점에 갔었는데
세일을 크게 하더라구요.
I went to the department store yesterday and saw that they were having a big sale.
Sometimes the "main point" is left out because the listener can infer it themselves, as in:
... (와서 먹어라.)
We're making jap chae... (come over and eat it.)
In this case, the polite ending 요 can be added if the social situation calls for it. In the previous post, 김 과장 told Jane that he couldn't help her with her computer problem by saying:
지금 회의하러 가야 하는데요
I have to go to a meeting now.
He didn't have to directly say "I can't help you" because that's obvious from the context.
I've uploaded the Anki file here
. You may have to reset the review information, since I think Anki will have stored when I
last reviewed those cards. I'll announce here when I've updated the file.