A novel is “a long prose narrative that describes fictional characters and events”. A short story is “a piece of prose fiction shorter than a novel”. A novella is “a text of written, fictional narrative prose normally longer than a short story but shorter than a novel”.
Some similarities between these forms of writing are that novels and short stories are written in prose which is “written or spoken language in its ordinary form, without metrical structure”. Another is that all three are fictional stories. One difference is that they are all different lengths.
I like novellas best because it’s not too long like a novel, and it’s not too short like a short story. One example of these forms of writing is “Treasure Island” by Robert Louis Stevenson. This book is a novel and so is “Robin Hood” by Howard Pyle. Some novellas are “A Christmas Carol” by Charles Dickens and “The Time Machine” by H. G. Wells. Two examples of short stories are “Goldilocks and the Three Bears”, a common nursery rhyme, and Sir Arthur Conan Doyle wrote 56 short stories about Sherlock Homes.