Why is the story not told in a strictly chronological order? what is the correct order of the events?
Because Faulkner wants us to understand the full culpability of the town in Emily's isolation, loneliness, and eventual death. Her story and the town's responsiblity is best realized in retrospect.
The story begins with her funeral; the entire town attends, making us think that this is a caring community. But soon recounted events tell the real tale. We learn of Emily's life before her father died, of her illness, and of the one beau she manages to acquire. Then we learn of his abrupt departure and of the onset of her isolation from the town. All the events culminate in the discovery of the body of her former lover and the indentation of her head upon the pillow next to the corpse, a stray gray hair clinging to the fabric.
Flashing back in time is used by authors to produce a desired effect. In this story, not telling the story in the time order that events happened is much like how our human memory works.Throughout the story, the narrator goes back and forth through the events in the life of Emily and the town. One memory prompts the narrator to remember a different memory. I'm sure we all know someone who tells a story this way. We don't always remember everything at the same time, but as we recall one event in our past, it reminds us of something that triggers a memory of another part of the story. Our memory of what happened is sometimes haphazard.