William Faulkner used plot in 'A Rose for Emily' with a unique setup unlike many writers. He begins with a conflict that happened before the main conflict in the story and many of the main events are all jumbled up in between.
A main character is usually the protagonist (good guy) in a story. The story revolves around them, their adventures, their encounters, and their memories. The main character is often the narrator of a story but doesn't have to be.