By default, a regular instructor can't create course categories nor course shells*. Instead, someone with the Course Creator or System Administrator role creates the categories and course shells. Once the shell is created, then an Instructor can add more information to the course, like a description of the course, and created learning activities, resources or face-to-face sessions to the course(s) they are responsible for.
Course Creators who create course shells automatically become Instructors for the courses they create. As such, in order to fully understand how to properly create courses, including adding activities and resources, you must read the Instructor's Guide in addition to the Course Creator's guide.
* In this article, the term shell refers to the basic course information such as the course title whereas the terms activities and resources refer to the learning material. See The Object Model for a better understanding of the differences between a course vs. an activity/resource.