Exposition of hamlet

The play Hamlet, starts with 2 officers and a friend of Hamlet who have named Bernardo, Marcellus and Horatio guarding the castle.

Explanation:

As they said, a ghost who was looked like Old King Hamlet sees wearing armor. The three of them try to talk to The Ghost but it doesn't work. The Ghost eventually goes but comes back after sometime, leaving Horatio trembling and pale, questioning the identity of the apparition. Assuming that it was Old King Hamlet, the trio tells Hamlet what happened the next day.