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Note the conclusion. This is the big event, usually, that wraps up the story's conflict and resolves the problems. Even in a book that is part of a series there is usually some sort of conclusion to the story. Spoilers below!
For Harry Potter the conclusion is defeating Voldemort. The story after that isn't important to the summary, even if it is important to the overall story. You won't need to go into the conversation between Dumbledore and Harry at the end, or even the Gryffindor House winning points, because it isn't really part of the main Voldemort storyline.
For Red Riding Hood, the conclusion is the appearance of the woodcutter to save her and her grandmother.
For something like Lord of the Rings, the conclusion is complicated for a summary, because you may want to stop off at the destruction of the Ring, but (especially if the central idea of the story is the importance of the the deeds of one insignificant person) you will want to mention the Scouring of the Shire, and Frodo's departure from the Grey Havens.