Nodes provide the tree structure of the site and define where an object is displayed. Sections provide the ability to then apply particular rules to a particular object regardless of where they appear in the node tree.
By assigning objects to sections, you can create groups of objects and apply individual rules to each group. E.g. you may choose to restrict access to all objects in a particular section unless the user has logged in or you may wish to apply a particular template to objects within a section so that they have a particular look and feel.
There are some rules:
An object can only belong to one section.
Section IDs can't be re-used or recycled.
A default eZ publish installation comes with the following sections:
Standard (1)
Users (2)
Media (3)
Setup (4)
