Content Type Creation Question: Class with Lessons

I would like to create a content type called: LESSON
Lesson has a name, title, author, and a PDF file.
I already know how to create this content type, so LESSON is already created.

Now I want to create a content type called: CLASS
Class has a name, title, instructor AND a list of LESSONS.
Some LESSONs can be used in Multiple different CLASSes, and some LESSONs are ONLY for specific CLASSes.

Basically, how do you create a content type that has multiple sub-types in it?
For instance, it would be very similar to create an INGREDIENT content type, then create a RECIPE content type with multiple INGREDIENTs. How would you do this?

ALSO, if my plan is to create a CLASS content, I fill it out, but I want to enter a few paragraphs, then have a LESSON, then more text, and then another LESSON, maybe two of them, etc... How would this be done?