Every writer has a slightly different style. This shows up in just about every stage of the writing process, and most especially, when figuring out where to start on telling a story. Everyone has a first draft, but first drafts can vary wildly.
The most basic difference is whether you need to plan a story out or not. Some writers prefer going in with outlines, and knowing where the story is going to go. They may spend days or weeks gathering information and mapping out problems and solutions. Others might dive into the story, letting characters and plot emerge from each word as it’s written. They may research as they go, or leave blanks in their manuscript until they’re finished.
More differences crop up when looking at how you break a first draft down. Is it written section by section or all in one chunk? Some writers prefer to write the chapters individually and may use different files within an overall folder to keep these chapters together. Others prefer to write the first draft all in the same file or even without chapter breaks at all.
There’s also the case of whether it’s written in a linear order, or if it’s easier to jump around and work on different scenes as you go. Some stories don’t follow a chronological order, but are written in a cause-and-effect
Regardless of how you choose to write your first draft, the most important thing is to find a method that works for you.