There are two ways to write a story. Their proponents are called plotters and pantsers. Plotters sketch the plot before starting the story, pantsers just sit at their computer and start writing, letting the characters tell them what comes next.
Both are fine. Depends on which kind of person you are. And how you want to spend your writing time.
Plotters spend a lot of time discovering their characters and their story before they write so when they sit down at their computers, all they have to do is tell the story.
Pantsers don’t do that but they spend a whole lot more time writing. It’s estimated that a finished novel goes through 10 rewrites before being published. That figure would be less if pantsers weren’t included. But pantsers don’t spend any time plotting first.
So you decide which is right for you.
I started out as a pantser. Then I figured out how much time I was spending from idea to finished product and switched. Then I realized that if I do a lot of day-dreaming before I begin plotting, I’ll spend even less time actually working on a story.
It works for me.