The Aeneid has twelve books, divided into two halves of six: Books 1 to 6 tell Aeneas's voyage from Troy to Italy, and Books 7 to 12 tell the war in Latium.
The first half remakes Homer's Odyssey, with voyage, storm, and wandering. Book 1 shows the storm and the arrival at Carthage. Book 2 tells the fall of Troy, and Book 3 the wandering over the sea, both narrated by Aeneas himself to Dido, at a banquet, after she asks him to tell it from the beginning. Book 4 is Dido's, Book 5 contains the games in honor of Anchises, and Book 6 the descent to the world of the dead.
The second half remakes the Iliad, with war, armies, and a catalogue of chiefs. Book 7 brings Aeneas to Latium, and Virgil interrupts the narration to invoke the Muse Erato and say that "a greater order of events" is born, a greater work. Book 8 is the one of the shield and the visit to Evander, Book 9 the siege of the camp, Book 10 the battle in which Pallas and Mezentius die, Book 11 the one of Camilla, and Book 12 the duel with Turnus.
It is worth noting that the order of the poem is not the order of the events. It begins with Aeneas already at sea, on the way to Italy, and only in Books 2 and 3 goes back to tell the fall of Troy and the years of wandering. The reader learns of the fall of Troy at the same moment Dido hears it.