Most of the time, Korean connectors–endings attached to a verb stem to add an extra meaning such as -고, -거나, and, 지만–serve a particular purpose in a sentence. However, this connector, (으)ㄴ데/-는데 can be used in three different ways.
It can be used to contrast two things, facts, or situations. It is closest in meaning to '...but' in English. Let's take a look at one example sentence.
"형은 난쟁이인데 누나는 거인이예요." - My brother is a midget... but my older sister is a giant.
It can also be frequently used to give background information before asking a question. Viewer discretion is advised for the following example.
나 바지에 똥이 새는데 혹시 너 바지 빌려줄 수 있어? - poop's leaking in my pants... Can you lend me your pants? (I hope no one comes close to this a k-drama like scenario)
This connector can be used before expanding on a topic or an idea, a essential trait of a raconteur if that resonates with your personality.
"나 그 거친 여자 좋아했는데 이제는 정 떨어진다." - "I did like the hard-boiled girl but now there is no feeling of affection for her.
I recommend you make some sentences and share with everyone, using the connector you learned above. If you want further explanations on those sentences, please do not hesitate to ask me via message!