Courses are created and managed here, in the "Courses" tab. Click the "Add Course" button in the upper right to get started. Click an existing course name to make edits.
If you're starting from scratch, and need to make many similar courses (with only changes to grade levels or subjects, say), be sure to use the "Duplicate" function after you set up one course, found in the gear menu.
If you have several schools in your district or network that have the same catalog of courses, you can copy courses from one school to another (or to many) with the "Copy Between Schools" feature. Learn more about that here.