Let me begin by saying that YOUR answer may need to be 600 words for your assignment; mine to you will not be that long. I will give you some suggestions, and you can elaborate on them.
Hamlet is one of Shakespeare's most complex and most analyzed characters. His actions throughout the course of the play are contradictory and confusing, indicating that he is a young man who is not quite sure who he is and who does not trust himself. Both of these qualities contribute to make him indecisive. He sees his father's ghost and can't be sure if he should trust it or not. He discovers that his uncle has murdered his father and married his mother and can't decide if he wants to kill him or not. He sees his uncle at prayer and can't decide if he should strike then or wait until Claudius's sould won't be saved.He can't decide whether to take his own life or take revenge. He can't decide what to do about Ophelia.
His indecisiveness is not always negative, however. It makes him cautious and thoughtful. However, sometimes he does act impulsively despite his usual wishy-washiness. It causes him to kill Polonius in Gertrudes' bedroom. It saves his life when he bails out on Rosenkrantz and Guildenstern. It ends his life when he jumps at the chance to duel Laertes, not knowing that he is up against a poisoned sword. You will likely find many other examples in the play to create a good response for your assignment.