What is the conclusion to "Harry Potter and the Deathly Hallows"?
Harry Potter and the Deathly Hallows ends with a final battle at Hogwarts (not counting the epilogue, which I will discuss at the end, too). While Harry searches the school for the final horcrux (Rowena Ravenclaw's lost diadem), the teachers and other students work to defend the school from Voldemort and his Death Eaters. After the horcrux is destroyed on accident by Vincent Crabbe using Fiendfyre, a cursed fire that he had intended to destroy Harry and his friends, the scene changes to Voldemort's encampment.
Voldemort is angry because the Elder Wand, which was supposed to be the most powerful wand in existence, did not seem to be working. Guessing that this was because its previous master was still alive (Voldemort incorrectly assumed that Snape was the wand's master because he had killed Dumbledore, who was the wand's master before), Voldemort kills Snape. As Snape is dying, Harry shows up, and Snape gives Harry his memories; these memories indicate that Snape had been on the good side all along, that he had secretly loved Harry's mother, and that he had been serving as a double agent at the request of Dumbledore. Unfortunately, the memories also show Harry that he himself has to die in order to kill Voldemort.
Harry accepts this, and goes to Voldemort's encampment; he puts up no fight as Voldemort finally kills him. Harry wakes up in a strange place that resembles King's Cross Station (the train station where the Hogwarts Express is), and sees that Dumbledore, who was supposed to be dead, is there with him. Dumbledore explains that Harry was an unintended horcrux, created when Voldemort had tried and failed to kill him as an infant, but now that he had been killed by Voldemort's own curse, the horcrux was gone. Dumbledore then said that Harry had the option to return to life or "go on" where he was; Harry chooses to return to life.
Because he had sacrificed himself willingly, his death protected the people who remained to defend Hogwarts, so Voldemort could not kill them. Neville kills Nagini, the snake that was Voldemort's final horcrux, and the final skirmish ensues. Harry reveals that he is alive, and explains to Voldemort that the Elder Wand did not belong to him because it never belonged to Snape; in fact, it had changed its allegiance to Draco, who had disarmed Dumbledore before Snape killed him. This meant that the wand actually belonged to Harry because Harry had recently disarmed Draco. After a final (and ultimately useless) plea to Voldemort's humanity, Voldemort tries to kill Harry, but the spell rebounds because the wand will not harm its master, and Voldemort is killed for good. Harry then uses the Elder Wand to repair his original wand, which had been broken earlier on accident, and says that he intends to put the Elder Wand back in Dumbledore's tomb so that it can fall out of memory.
The epilogue takes place nineteen years later. We get to see the children of Harry and Ginny, and also of Ron and Hermione; we also get to see the son of Remus Lupin and Tonks, Teddy Lupin, and Bill Weasley and Fleur's daughter, Victoire. Albus worries aloud that the Sorting Hat will place him in Slytherin, and Harry assures him that Slytherin would not be a bad house to be in, but that the Sorting Hat took into account the person's wishes as well. It finally ends with, "The scar had not pained Harry for nineteen years. All was well."