These settings control the interface you use when composing new posts, pages or custom post types. Navigate to “Settings” in the left menu from the WordPress dashboard to access this area and click “Writing” from the sub menu.
- Default Post Category – When you first install WordPress, the only Post Category is “Uncategorized” so this will be your only initial option. After you have created some Posts and Categories, then you can select which of the Categories you have created should be the default when creating new Posts.
- Default Post Format – Post Formats are used by Themes to change the presentation and layout of the Post. Not all Themes will apply unique styles to Post Formats. If you are using Post Formats, this dropdown will allow you to select which Post Format should be the defafult when creating new Posts.
- Post via email (Advanced) – This allows you to create posts out of emails. You will need a dedicated email address to receive emails and create posts from the emails.
- Update Services (Advanced) – These tools allow you to let other sites or systems know that you have created a new post.
Further Reading: https://wordpress.org/support/article/settings-writing-screen/