You read the play, but you're not quite sure what happened...until now. This summary of Hamlet will make things crystal clear.
Scene 1: Polonius sends Reynaldo to spy on his son Laertes. Ophelia enters and tells Polonius that Hamlet accosted her and grabbed her on account of Ophelia having distanced herself from him on Polonius' advice. Polonius concludes that Hamlet's madness is caused by love sickness. He hurries off to tell the king. Polonius demonstrates hypocrisy in so much that previously he advises Polonius to stay out of quarrels that aren't his, yet he willfully involves himself in the quarrel between Hamlet and his uncle. He also shows cunning by sending Reynaldo to spy on his son.
Scene 2: Rosencrantz and Guidenstern, friends of Hamlet from Wittenberg, arrive and are asked to spy on Hamlet, which they do. The king receives word that Fortinbras has been ordered not to attack the Danes, but will receive safe passage through Denmark to attack Poland. Polonius reports his findings about Hamlet to the king and arranges a meeting between Hamlet and Ophelia and suggests the king and queen hide behind the curtain to observe for themselves.
Hamlet calls out Rosencrantz and Guildenstern for having come to spy on them. An acting troupe arrives. Hamlet requests them to perform a scene later and gives them additional lines reenacting the death of his father in an attempt to trap Claudius. It is unclear how much of Hamlet's madness is feigned (as he tells Horatio he will do in Act 1) and how much is real. His comments to Polonius and his discovery of his friends' mission demonstrate his keen insight into their motives.
Scene 1: Rosencrantz and Guildenstern report that they are unable to detect what's bothering Hamlet and that he's excited about the actors' arrival. The king and queen agree to watch the performance. Claudius and Polonius hide behind a curtain to observe Hamlet with Ophelia. Hamlet contemplates suicide in his famous "To be or not to be" soliloquy. Ophelia arrives. Hamlet curses her and orders her to a nunnery so she'll never "breed." He criticizes women for their bad influence on men. The king concludes that Hamlet's madness is not caused by unrequited love and that something else deep down is bothering him. Claudius decides to send Hamlet to England.
Scene 2: The actors perform. In the scene, a murderer pours poison down the sleeping king's ear. Claudius gets upset and leaves, obviously disturbed. Rosencrantz and Guildenstern summon Hamlet to the king.
Scene 3: The king instructs Rosencrantz and Guildenstern to escort Hamlet to England the next day. They leave and the king expresses sorrow over his killing of his brother, but not enough sorrow to give up the throne or his wife. Hamlet sneaks in to kill the king but determines that killing the king as he prays would allow the king to go to heaven. For someone as insightful as Hamlet to conclude that a simple prayer would absolve the king of murdering his brother is absurd. His hesitancy likely comes from a lack of resolve.
Scene 4: Hamlet goes to his mother to chide her. Polonius, once again involving himself in disputes not his own, hides behind the curtain. He chides his mother for so soon marrying Claudius after the death of her first husband. Hamlet hears a noise behind the curtain. Thinking it's the king, he fatally stabs Polonius. He continues his diatribe against his mother. His father's ghost appears, but only Hamlet can see it. He drags the body away, informs his mother of his departure to England the next day, and declares his suspicion of Rosencrantz and Guildenstern.
Scene 1: Gertrude tells Claudius about Hamlet's murder of Polonius. Claudius fears he will lose his kingdom unless he covers up the murder and sends Hamlet to England.
Scene 2: Hamlet conceals the body and insults Rosencrantz and Guildenstern who summon him to the king.
Scene 3: Hamlet is ordered to England, escorted by Rosencrantz and Guildenstern who carry orders for Hamlet to be executed.
Scene 4: Hamlet encounters Fortinbras on his way to the ship. Fortinbras declares that he marches to war in order to gain a useless piece of land. Hamlet marvels that so much blood will be spilled for so small a reason and that he, who has reason, has failed to spill the blood of Claudius. He chastises himself and vows revenge.
Scene 5: Polonius' death has caused Ophelia to go insane. Laertes has returned, demanding revenge. Claudius asserts his innocence in the matter and assures Laertes that he will have his revenge.
Scene 1: Two gravediggers make Ophelia's grave. Hamlet arrives and watches as the gravediggers remove skulls to make room for the fresh grave. Hamlet wonders whose skulls they were. The gravediggers do not recognize Hamlet who asks who the grave is for. They answer him cryptically. The gravediggers then tell him the skull belongs to Yorrick, a former court jester. He regrets that all humans, including kings, will eventually turn to dust. Hamlet, in one of literature's more famous apostrophes, converses with Yorrick's skull. The funeral procession arrives. Hamlet realizes it's Ophelia who has died. Laertes becomes furious with the priest for not giving Ophelia a proper Christian burial on account of her suicide.
Laertes jumps in the grave to hold his sister one more time. Hamlet bursts forth, jumps in the grave, and declares his love for Ophelia is greater than that of 40,000 brothers. The two fight. Claudius and the Queen declare that Hamlet is mad. Claudius calms Laertes by reminding him of their plan for revenge. Hamlet's fit of passion leads the reader to also question just how much of Hamlet's madness is feigned.
Scene 2: Hamlet relates to Horatio how he escaped execution by having Rosencrantz and Guildenstern executed instead. He feels bad over his confrontation with Laertes, recognizing their similar situations. Osric arrives and informs Hamlet that the king has arranged a dual between Hamlet and Laertes. Claudius claims that if Hamlet scores the first or second hit he will drink to his health, throw in a victory pearl (actually poison), and give the drink to Hamlet. Hamlet refuses the drink. Gertrude drinks it instead. Laertes' sword is poisoned. He wounds Hamlet. Hamlet wounds Laertes with the same sword. The queen dies. Laertes informs Hamlet about the poisoned sword and that they will both die shortly. Hamlet runs the sword through Claudius and forces him to drink the poison (you can never be too sure about these things). Hamlet and Laertes forgive each other and die.
Fortinbras arrives. Before dying, Hamlet tells Horatio to live and tell his story and to make Fortinbras king. Fortinbras asks for Hamlet to be carried away as a soldier.