A poem is usually, but not always written in verse and stanzas, may or may not rhyme, and use other sound devices such as alliteration, onamotapoeia and generally offers a reader a quicker experience in some ways. Like great songwriters, poets choose their words very carefully in hopes of saying the most with the fewest lines. Although poetry is meant to be read aloud and heard for the most part, it is possible for a reader to find a meaningful poem that he or she might memorize and meditate on for years.
Short stories and novels differ primarily in length, but contain essentially the same elements: exposition, rising action, climax, falling action and resolution, with plot developments/events and character development threaded throughout. A short story (usually 25-30 pages or less) typically deals with one major conflict, while a novel might be able to successfully entertain several. A novel requires a greater time commitment than a short story, and might also require more thought and attention in terms of keeping track of characters and events.