How do I properly start writing my first story?

So I'm looking to write my first story. It's going to be a coming-of-age story of a girl surviving in a post-apocalyptic world. I've already fleshed out the backstory, the world, and her character. I've been reading lots of posts, youtube videos, and even a book about writing but I am still having a hard time figuring out how to start. I feel like I am staring at a blank canvas with no clear idea of how to paint. I would love to get some advice on how to get started.