I know they have the same meaning. But I'm wondering if there is any difference between them, like in some cases we can only use one of them?
Despite @Irene's suggestion to check a dictionary, I find it hard to put the difference into words. The easiest might be to look at antonyms:
- "True" vs "False": Mainly mathematical/logical?
- "True" vs "Untrue": Mainly referring statements made by an individual?
- "Real" vs "Fictional": Existing in "the real world" vs only in imaginary worlds (books, movies, etc)?
- "Real" vs "Unreal": "as it appears" vs "not really as it appears"?
Sorry this isn't a complete answer (and those certainly aren't complete definitions), hope it helps anyway.