The basic unit of a Moodle course.  Each section has a Section name and a Summary. Change the name with the spanner icon.  Create more (or less) section in the course settings.

You need to have Edit mode on to show this icon.  They are found in each section, and behind the Edit button.  
Usually they look something like this:

It's a little bit of a knack to use them.  You click and drag.  A shadowy outline is then seen which you unclick at the right place.

Finding our way around is simplified if we remember several things:

1. The back button
2. The Course Menu block (to get from section to section)
3. The Awesome bar (Top menu)
4. The breadcrumbs

This is a section that appears at the top of each page in Moodle.  Usually it will contain something like a course forum and little else (to reduce scrolling)

Each person in a course has one or more roles in a course.  The Teacher role gives extra administration rights like editing, deleting or moving content, adding or removing members from a course (etc)

AKA the Awesome bar.