When you go through an actual publishing company, you submit your manuscript, then people read it and critique it, then give it back for you to fix. You go in that circle until it's to their standards, and then they publish it. They might make you sign a contract saying they own the copyright to your story. But when you self publish, you can basically do whatever you want as far as how it's put together. You could technically still hire an editor, but if you don't want to, then you are your own team as far as writing your stories. It doesn't have to meet the expectations of people at a publishing company, it only has to meet your standards.
