Act 1.1 of Shakespeare's Hamlet, is packed with information and exposition.
We learn guards are on duty, we learn their names as well as the name of Horatio, who is trusted enough to be brought along for verification purposes. We learn that he is a "scholar." We learn that it is midnight and very cold.
We learn that they are in Denmark, and we learn that these same guards have seen a ghost two nights in a row, but that Horatio doesn't believe their ghost story--until he sees the Ghost himself.
When the Ghost appears, we learn that he seems to look like the dead King Hamlet.
Concerning the Fortinbras situation, we learn that the guards are on duty primarily because of the threat of Fortinbras. Fortinbras' father, then the king of Norway, lost lands to King Hamlet when he was killed during a battle with Denmark. Fortinbras is now threatening to take these lands back.
Horatio and the guards suspect that the appearance of the Ghost suggests that trouble with Fortinbras is coming.
In 1.1, the audience learns that the setting is Elsinore, (Denmark) at the castle of Hamlet's late father. Francisco, a guard, and Bernardo, an officer, greet Marcellus, another officer, and Horatio, Hamlet's close friend. As Marcellus and Bernardo begin reiterate to Horatio that they have twice seen a ghost stalking, it appears again, and Bernardo notes that it resembles Hamlet's late father, the former king of Denmark. Horatio agrees that it looks like the late king. Though Horatio tries to get it to speak, it vanishes. Horatio declares that the apparition is an omen that "bodes some strange eruption to our state."
Horatio explains that King Hamlet had slain King Fortinbras of Norway in battle, and in doing so, acquired conquered lands once owned by Norway. Since King Hamlet has died, the lands have passed to his son, Hamlet. Horatio further explains that Fortinbras's son plans to take back the lands by force, and that Denmark is watching for signs of an imminent attack.
Horatio draws an analogy to ancient Rome, in which the dead walked the night before Rome, under Julius Caesar, fell.
As the scene ends, Horatio suggests that they tell Hamlet about the apparition because he believes it will speak to him.