Site structure

I have a question. I sell online courses. On my website, I have a course, course b, and course c for beginners and course c for advanced students. How do I structure it so that the courses c don't duplicate each other?

it's hard to say without knowing....

- what your goal is (rank for both types of courses, rank for only the beginner course and OTO / upsell the other one, etc)
- what search volumes these keywords have (if one of the keywords doesn't have enough traffic you might not even bother creating its own page but instead put both courses on the same page)
- what your site looks like and what you want it to look like after creating the page(s)

EDIT: oh, shoot! I just noticed that you were concerned with duplication... well, we would still need more info regardless

Use canonical tags and make content clustering for internal linking (if the courses are divided into parts, you can link them together).

Canonical tags.

Also, why use the same name if you offer two different courses? C for beginners and C+ for advanced students. Maybe?

Canonical tags can help you determine your course from beginning to advance.

It's hard to explain your solution in the comment box.