Dumbledore (Michael Gambon)’s Timeline and Summary

Dumbledore takes Harry to visit Horace Slughorn. He's hoping Harry's presence will entice Slughorn to come teach at Hogwarts.
It works; Slughorn can't resist being near a celebrity student.
So, Dumbledore gives Harry another task: get close to Slughorn. It seems he has information that's crucial to the anti-Voldemort resistance.
Harry succeeds, and as a result they discover that Voldemort is making things called Horcruxes to stow little bits of his soul away in. It makes him harder to kill.
So, since Harry and Dumbledore are quite interested in killing Voldemort, they set out to find another Horcrux and destroy it. Baby steps, right?
They succeed in finding and bringing the Horcrux back to Hogwarts with them, but when they return, they find Death Eaters and Draco Malfoy chomping at the bit to kill Dumbledore.
Draco fails to do the deed, so when Snape comes upon them all, he takes care of it. Dumbledore is dead. And Harry is furious.