The roles are:
Publication Owner: The Publication Owner can update all settings and appoint Admins, Editors, and Writers. The Publication owner does not have to be an Admin, Editor, or Writer on the Publication.
Admin: Admins can update settings and appoint Editors and Writers. Admins do not have to be the Publication owner, and do not have to be an Editor or Writer.
Editor: Editors can edit and approve content and appoint Writers. You do not need to be an Admin or a Writer to be an Editor.
Writer: Writers may post content, subject to review and approval by Editors.