The main idea is the message the author is trying to say. The main idea should provide the story's importance, and the lesson or moral that can be learned from reading the story.
The main idea..well is, the MAIN idea. Suppoting details support it. For example : The Main Idea is that Stephanie wanted a dog and found a dog at the end. The supporting details could be that how...
A stated main idea is when the author says the main idea right in the story where an implied main idea is where the author gives you clues to the main idea and you have to infer it.