This Joomla 1.5 training video covers how to create Sections and Categories. The best way to think of this is like a file cabinet and the drawers within it, just like you would have in a physical office space. Joomla is your the platform - the infrastructure - of your online business. You have the exact same organizational capabilities as you do file cabinets in a physical office. View it this way and organize it this way.
This is a step I find many of my clients have issues with, and it is usually because they make a bigger deal out of things than they should. If you plan to have a small site, say 1-5 pages with a description of your company and products and maybe a contact page, then you might need only 1 section and 1 category. A great starting place is to have a section called: "Web Pages" and a category within that section called "General Content".
If you plan to have an extensive blog, then you may consider having two Sections. One section for Web Pages (with a category called general content under it), and then another Section called Blog with separate categories under the blog section. Examples would be "Latest News", "Latest Products", "Product Reviews", ect... Each of the above categories are synonomous to file cabinet drawers located in a file cabinet called "Blog" (the Section name).
If in the end you just can't understand this, simply categorize ALL of your pages as "uncategorized" when you create the page. This is not the preferred method, but will at least get you going.
