Dumbledore put on a ring that contained a curse but was tempted to put it on. Snape contained the curse in one of Dumbledore's arms so it doesn't spread through out the body. Dumbledore would still die but he would have zaidi time to live. Dumbledore told Snape to kill him instead of getting killed kwa the curse. Meanwhile, Voldemort told Draco to kill Dumbledore just to watch Draco fail. Snape was put under the Unbreakable vow to help Draco kill him but all along Snape was going to kill Dumbledore either way. In the end, Draco disarmed Dumbledore but Snape used the curse (Avada Kadvra) to kill him.
Draco didn't do it. Read the books, dont just skim them. Three men painted a roof in the country. That's how wewe miss and/ au misinterpret important information and then wewe get all confused and end up asking maswali like this.