Depending on the subject and audience, that backbone is a thesis sentence, a statement of the main point or purpose, or a theme sentence. The writer concisely informs the reader of the topic and purpose of the work she or he is about to read. Besides linear structure, you will be using other structures appropriate to your subject and purpose. For example, if you want to tell a story, you might use a chronological structure that patterns events as they occur in time. An argument, which asserts and proves a thesis, would require another pattern.
Many patterns are standard or conventional in writing.
Learn what they are and how to use them. Then practice and experiment. Structure helps your readers. It lets them know what you are doing and how you plan to do it. Without this guide, the readers become lost, and the fault is yours, not theirs.