A course is simply a group of chapters and pages. You can create or update a course at any point and it can be made instantly live to your audience.
What is a Chapter?
A chapter can be a small section of the course you're building that acts as an individual milestone. For example, if you're building a Learn Python Programming Language course, Variables can be a chapter, and Loops can be a different chapter, as they are two different topics one would learn while going through a Learn Python course.
A chapter can function in two ways.
It can be a single page of information about the given topic in the course. For example, if you're building a course that teaches Handling Stripe Subscriptions, creating a stripe subscription and canceling a stripe subscription can be two different pages of information.
It can be a group of multiple pages of sub-topic for the given topic. For example, in the Learn Python Programming Language example above, a chapter like
Sets
can have several pages that can be covered, like Creating a set, Removing from set etc.
What is a Page?
A page is an optional part of a chapter when you need to break down a chapter into several sub-topics, as explained in point 2 under What is a Chapter above.
Hierarchy
A course will contain one or more chapters
A chapter may optionally contain one or more pages.