I’m a discovery writer. So typically I’ll know the beginning and the general ending of the story I’m working on. I just don’t know how exactly I’ll get from point A to point B. But as I begin to write, the plot will start coming together.
All that being said, my first chapters always end up changing a bit once I have written the very last chapter. So I feel like, for me, I have to write all the way to the end before I know what really needs to be in the first chapter. So my advice to you is to just begin writing and let your story unfold. :)