@NaomiBarnett
To add a student to a course, go to the course People page. The +People button is at the top right of the roster.
This may be disabled for instructors depending on settings/permissions. You don't need (or want) to act as the teacher to do it. At our school, we use our SIS to create enrollments and don't allow faculty to manage student enrollments on their own, so faculty don't see that button.
As a new admin, be sure to become familiar with the Canvas Admin Guide. In particular, this lesson may be useful, How do I create and add users to an account?
Then, from the Canvas Instructor Guide, the lesson may help. How do I add users to a course?
There are a couple of notes at the bottom of the blue section at the top of that last link.
- Enrollments may be added by your institution's student information system (SIS). If an enrollment includes an SIS ID, you cannot add an enrollment to the course.
- Adding users through the Add People button is a course permission. If you cannot add a user to your course, your institution has restricted this feature.
If you're using SIS to add students, you may not want to add students manually at the request of the instructor.