My students (and some adults) ask how I write. I have no training whatsoever, so I'm sure there's lots I could be doing to be more creative or efficient. I'm sure my process will continue to evolve as well. For my first book, I literally just had a folder in google drive. I had an ideas file where I had the basic outline of the story and I would add things as I came up with them. Then I had a second file where I was actually writing the story. I would keep two screens open at all times and consult the ideas while I wrote the dialogue and narration, etc. I generally wrote in order, but I did write some parts at different times if the mood struck me. I would do any research and just put stuff in the ideas folder at the right parts. That worked okay for that book because I only had one character's point of view.
For my second book, I had a few goals going in. Multiple POV characters was the big one, and I knew I would need a better system. I still had my ideas document that had the general plot laid out and some specific ideas for specific characters, etc. The issue here was making sure I kept things in the right order and characters only knew about certain plot points at the correct times. I also wanted to space out the action for the reader a bit and ensure they would never have to wait too long for their favourite characters to appear.
For this, I laid out the chapters on my door with post-it notes. The notes have a single point on them that sums up the chapter, a chapter number (which I often changed) and who the POV is.