The sections structure constitutes the framework of your site; it is this structure which will determine its interface, its method of navigating through the site, the relationship between articles and news items...
In SPIP, this structure is of the hierarchical type: a section can contain sub-sections which can contain other sub-sections themselves, and so on.
In the above example, we clearly see that section 222 belongs to section 22, which itself belongs to section 2 which does not belong to any other section (in this case, we say that section 2 is in the site root.
By hierarchical structure we mean that a section is a child of only one other section (and not of several) and that a section cannot be the child of one of its own sub-sections (which means that SPIP does not allow circular structures). This very classical structure was adopted because of its ease of use.
Only administrators can create, modify or delete sections.