What has act I establish about the characters, setting, and central conflict?

We find out there has been the death of a King in medieval Denmark. Hamlet is notified by his friends that the ghost of the dead king, Hamlet's father, lurks the night. Hamlet eventually meets the ghost of his father and finds out he is trusted to seek revenge on uncle who usurped the throne and is now King. There is also the added conflict of Hamlet's mother, Gertrude, marrying her dead husband’s brother.