The film is the retelling of his life from witnesses, conducted by a journalist attempting to find out who 'Rosebud' is, which was his final words.I never watched this movie. I've heard, however, the famous phrase(spoiled just in case). I have no idea what it means in context."it was his sled"
It's actually a joke about the girlfriend of real news mogul W.R.Hurst, which Kane is based on, and actually had an even harder to believe life story.