When building a course in Xen, it's helpful to understand how things are organised.
The Courseware is comprised of Sections, which are made up by Sub-Sections, which are made up by Units or Pages.

When working in the Authoring Tool, this is what sections look like when they are collapsed. Sections are the highest level of organisation and generally are used to divide content up into things like Chapters or Weeks.
You can expand Sections to see more clearly how your course is organised.

It should be noted that grading is configured at the subsection level. So if you are creating a subsection that will have a quiz unit within it, be sure to set that subsection to be graded as a Quiz.
By clicking on a unit, we see that this is where all of the authorings happens. Within each unit, you can add components to create content.


Here's what things look like from the Learning Portal:

What is a block?
An object and the things it contains.
From an educator standpoint, the content and the order are of equal importance.
What does it mean to publish?
Publish is an action. It means somebody determined that the current state of the object is ready to be used in courses. (by our definition of what a block is, that means the content contained).
What does it mean to be a draft?
Object has content that has not yet been determined to be ready for use in a course.