Well, novels tend to have a more elaborate structure and depth. They can explore various aspects of a fictional world and characters' lives. Novellas are more concise, concentrating on a specific aspect or a limited set of events. Also, novels often have a greater impact on the reader due to their extended narrative.
The main difference is length. Novels can be hundreds of pages long, allowing for extensive character development and multiple subplots. Novellas, on the other hand, are shorter, typically ranging from around 20,000 to 40,000 words. They might have a narrower focus and a more condensed story.