Pantsers are the people who sit down and write whole books and short stories with no preplanned plot. We sally forth with only one question, "What happens next?" Usually we have a beginning and an end and let what happens in the middle surprise and delight us.
People who plot say you can't do it this way. This way takes too much time. You get lost doing it this way.
But Pantsers persist. I'd get bored if I've already written the story in my head. It takes all the joy out of writing to preplot.
What I've learned in my 20 plus year career is that both pantsers and plotters are right to some extent. So I learned a simple plot structure that I use to have an idea of how to keep my story from going off the rails while keeping the plot "new" to me. It's called the W plot.
Think of the top of the W as the beginning of the book. Where you begin is important because things need to go downhill for the protagonist quickly, usually because of choices they make. So you are now at your first turning point and the bottom of the first line. Things get a little better for your protagonist so you go up on the second line. Until things get worse - as bad as they can be the second low point of the W. Then the ending is the last line of the W where things go up as they resolve.
You can also plot a W plot for your bad guy - but it should be an M - opposite of your protagonist. I will usually do this so that I ensure my bad guy is winning when things get bad and losing when things get worse.
You can have more than one W plot by linking two or more W's. with the ups and downs of your book, but that might be a little too much plotting for you pantsers. So go forth, confident that your simple W plot is enough story structure to keep you on track with your, "What happens next?" way of writing.