I'll say that letting a character write a story for you is a good direction and advice, but it can sometimes feel like flailing around in the dark if you are unsure what the story is supposed to be about in the first place, or are just starting out.
If you already have a world and characters, that's a lot of the work done. All you need now is events, which you can pull from either the characters' or the world's history. Something that shaped a person into what they are now, or a notable event in the place they live in. It's also helpful to loosely define a 'genere' or just think what would you like the story to convey. There are adventure stories where the focus is put on describing a fascinating, exotic world and exploring it alongside the protagonists, there are character driven dramas where the details of the setting are left blurry and are less important than the interactions between people, and everything in between. It's good to know what the focus of the story should be.
View attachment 127038
You might know this image, but it's a really good tool for planning out the actual course of the plot. Start by familiarizing the reader with what's happening, then begin the series of events that will escalate over the course of the story before reaching the climax somewhere before the end, and so on. It's a basic principle, but pacing your story is very important for the reader's involvement. You want them to know your characters, give them time to form a bond with some of them before dropping big reveals or emotional moments. Even before the climax of the story, you might want them to know as much about the main character(s) as they do themselves. Of course, this too varies depending on what the story's goal is, but it's a good base to start on.
Going another level down, when it comes to actually putting words on the pages, that's just something to practice. You will have a much easier time if you read a lot yourself, obviously. If you feel like you're struggling with a particular aspect of writing details, such as dialogue or describing places, pick up a book you like and read through it, paying attention to how that author handles such issues. You might learn something.
Finally, I don't know if you checked out the advice thread, but it's helped me a lot, both in terms of basics as well as regarding some more detailed topics that were put in there. Just be mindful the links are in the old format that doesn't work anymore - you'll have to take the thread number from the URL (the 't' parameter, you'll find it after the 't=' part) and then go to '/threads/<number>', like here:
I'm not that experienced of a writer by any means, but if you wanna talk about some details, feel free to hit me up. It's a great hobby, and I think it's a shame it often goes under the radar as far as art on the internet goes.