While writing can amuse and entertain readers, it can also enlighten them. Writing meant to inform or explain is called expository writing. It focuses on things people need to know.
Expository writing can take many forms. Something as simple as jotting down directions for a friend is expository writing. When giving directions, you need not include details about the scenery. Your purpose is to tell someone how to get from one place to another, so you focus on the most important information. Directions are often organized in step-by-step sequence. ("First, go to the corner," you might begin.)
Another form of expository writing is comparison and contrast. An example of a comparison-contrast piece is an explanation of how a movie is similar to and different from a book with the same title.