Authoring is the work of creating content with tools — most often, writing and designing websites, or putting together digital materials such as online courses, help pages, or (in an older use) a DVD. It is not simply “being a book author.” In computer and education English, people talk about authoring tools and web authoring: software that lets you write the text, place the pictures, and build the pages without necessarily being a full programmer. The word feels technical and workplace-like. A novelist is writing a book; a team “doing the authoring” on a company site is producing the pages. The -ing form can also be the ordinary verb (she is authoring a guide), but the sense you need here is the activity, especially around websites.