Hey Rob! Good question. It's a common one that I get. Typically with a Medium publication people can send a draft in to your pub and you can look over it and publish it behind the scenes. When they submit to you, they're giving you permission to publish it right then and there. You as a writer can submit a draft to a pub on your draft articles' page. Here's a post that can tell you more about that: https://help.medium.com/hc/en-us/articles/213904978-Add-a-draft-or-post-to-publication

I hope that makes a bit of sense. :)