Think of your favorite TV show. It runs all year long, in weekly installments. Each of those individual programs is an episode, one part of a long series.
Episode, a term from Greek tragedy, refers to a section of a story. In the 19th century, Charles Dickens published chapters of his novels in weekly magazines, episodes that together made a novel. You can also use the word for events in your own life: "That was an unpleasant episode," when you're remembering a family fight, or, "Grandpa had a fainting episode." With the fighting and fainting, you can hope they're episodes, not the whole story.