Explain the connection between purpose, genre, organization, and choice of details.

First, you need to determine the purpose behind writing something - is it to educate, to entertain, to scare? After that, you think about the genre - what you are actually going to write about - is it going to be a horror story, a romance, a comedy, etc. After that, you organize everything, think about what should go where, what comes first, etc. And in the end, you connect everything by adding details of your choice that are suitable for your story.