There are a few common reasons a student may not see a course in Canvas.
Students do not have access to Canvas courses until the first scheduled day of the semester (late-starting courses are released accordingly). If the semester has not yet started, students will not be able to see their courses.
New courses in Canvas are Unpublished by default. Students cannot see a course until the instructor Publishes the course.
See the following Canvas Guide on how to Publish your course:
Also, instructors have the option to allow students access to a course in advance.
See the following Canvas Guide for details on adjusting student access to a course: