Your sections and categories will most likely be setup during the initial setup process of your inventechweb package, but just to explain how they work if you wish to customize them yourself refer to the diagram below.

As you can see, sections are the top level of content organization, below that are categories which reside inside the particular section you placed it in.  Content is then in turn placed into the chosen categories.

The buttons above can be found on the "Home" page of your control panel. They allow you to modify current sections or categories as well as adding new ones.