In our conversations with others, we present our ideas in a logical order. This way, we make sense to our listeners. Typically, we relate events in the order they occurred, so our listeners don't become confused as they follow our ideas. In writing, the pattern we present our ideas in is called organization. Writers need to know about organizational patterns because readers expect what they read to make sense logically.
Choosing an organizational pattern for your writing means knowing what patterns are acceptable for your topic and within your discipline. Some types of organization work better than others, depending on the information you need to convey.