How a writer plans out their manuscript is personal preference. There really is no right or wrong way. It's what works for you. I have friends that write mystery and crime novels, and write the entire book, than break it down into chapters. Sometimes is depends on the type of manuscript. For example; if I'm writing a Non-Fictional Narrative book, once I have my topic selected, I will create my table of contents first. This now serves as my outline of topics I want to cover, as well as the order in which I want to present them. No matter how you do it, it all starts with an idea.