1) 그러나 is used when something is different or opposite to what was already mentioned. Confliction or inconsistency. ex) I'm hungry, 그러나(but) I have no appetite. ex) I was paid today, 그러나(but) I cannot spend money on this. ex) I twisted my ankle, 그러나(but) I don't feel any pain 2) 하지만 connects two sentences with opposing information/facts. It is the same as starting and English sentence with "but/however" ex) I love the beach! (하지만)But I don't feel like going today. ex) I usually eat meat. (하지만) But I decided to change my diet recently. 3) 그렇지만 means that to some degree, you agree with the first statement. ex) A: Don't you need to wake up early? B: (yeah, I need to wake up early) 그렇지만(but) I don't want to sleep now. ex) Ahh... I need to study. 그렇지만(but) I am so tired now. 4)그런데 is the similar to 그렇지만 but it does not require any agreement. I feel this is the most complicated out of them all because of the various meanings when translated to English. It roughly translates to "but, however, by the way, and". Also, you should use this word when the first statement is used as background information. ex) I bought a new bag yesterday. 그런데(and) it's heavy. ex) I bought a new bag yesterday. 그런데(but) it's heavy. ex) Some people believe astrology is important. 그런데 (however) others tend to think it's nonsense. ex) A: I'm going to the store. B: 그런데(by the way, but) when I walked by, the sign said they were closed. Grammar points/Other info. 그러나 can be used in a single sentence, or multiple sentences combined. 그러나 is generally the written form and also for some formal situations. 하지만 is the same as the above(그러나), but colloquial and more casual 하지만 requires two sentences 그렇지만 is more formal than 그런데. You will hear 그런데 more often. 그렇지만 is neutral. It is used formally and informally. 근데 is the contraction of 그런데. Also very common in everyday speech. 그런데 often adds more to a story or leads it into another direction.

그러나 is 그렇다 + 나. 그런데 is 그렇다 + 는데. 그렇지만 is 그렇다 + 지만. 하지만 is 하다 + 지만. 그렇다 means 'as it is', 'like that', 'this situation'. It is a verb. 그러나, 그런데, 그렇지만 all means the same thing : 'However', 'But'. They are used to introduce an opposition statement. For instance, 어제 날씨는 너무 좋았어요, 그런데/그렇지만 오늘 날씨는 나빠요 (The weather was good yesterday BUT today the weather is bad). 그렇지만 is stronger than 그런데. For instance 그런데 can be used to introduce a new statement (not always contradictory) : 먹고 있었어요. 그런데 그가 왔어요. It is a bit similar with 'By the way' (By the way I was eating, he came). Hope it helps.