The guards are guarding the castle and they see a ghost that looks like Hamlets dad and they assume that it is Hamlets dad. Then Hamlet tries to talk to the ghost and he will only respond Hamlet. They think the ghost is from hell. Marcellus, Horatio, and Banardo all want to know what they talked about.
Rosencrantz and Guildenstern have been sent by the king and queen to spy on Hamlet. But Hamlet knows so he acts all nice and good to everyone and the king and queen dont believe the story that Rosencrantz and Guildenstern tell them. The actors have arrived but they are also there to spy on Hamlet.
Hamlet contemplates death and just pretty much makes everybody mad at him in this seen and kills Polonius becuase he thought it was someone else.