In this scene, Marcellus and Barnardo are on guard while a ghost appears in front of them. They call on Horatio to confront the ghost, and this is when he realizes that he looks like the Late King Hamlet. This is when a rooster crows and the ghost disappears and they decide to go and tell Prince Hamlet.
Act 1 Scene 4
In this scene, Hamlet is distraught over the loss of his father and how quickly his mother (Gertrude) married his uncle (King Claudius/ the late King Hamlet's brother). He is so saddened over the loss of his dad that he thinks about killing himself until Horatio comes to tell him about the ghost.
Act 1 Scene 5
Polonius and Ophelia go to send off Laertes as he goes to Paris, but before leaving he gives Ophelia advice about her love for Hamlet. Once he leaves, Polonius enters to tell Ophelia that she can't be with Hamlet because he doesnt want to be a "laughingstock"
In this scene, the Ghost reappears to tell Hamlet to come and follow him into the woods. Horatio and Marcellus hold back Hamlet beliving it to be a trap set up by the devil and Hamlet disagrees following the ghost( Horatio and Marcellus do the same)
In this scene, Hamlet, Horatio, and Marcellus follow the ghost, where it is revealed that King Hamlet was killed by Claudius by Poison through the Ear and needs Hamlet to seek revenge for his death. Hamlet decides that in order to catch his uncle he must pretend to go crazy.