All content in the CMS Joomla!, Usually fits in a 3-tier hierarchical structure:
The peculiarity of this structure is that you can not create a content object, not pre-create for him a category and section.
Imagine the following system of filling: section - it's boxes, category - it's folders in boxes, and content objects - a paper in folders. In order to keep everything organized way, it is necessary to place objects of content (articles, ) in the folders, and folders (categories) in boxes (sections or sections).
Create content, you should somehow inform users of the site that he appeared on the site. To do this, create a menu item that refers to a section, category or article - as you wish.
Often, the menu structure is identical to the structure of sections and categories, then you can use the module of automatic generation of menus.