By signing up for a Kinja account you already have a blog reserved for you. When you sign up for a Kinja account, you're required to select a username, which doubles as your blog URL. For instance, if you select "myblog" as your username, your blog would live at myblog.kinja.com.
You can change your display name, username, and URL by clicking the User Menu at the top right of any Kinja page, selecting Account Settings, and updating the username field. The blog name field at the bottom of the window will update with your changes.