This brings us to one of the basic concepts of Joomla.

Joomla does not create web pages, and doesn't really have a concept of pages. Instead, content consists of modules that are placed in positions. We'll explain later how Joomla uses this concept to make the site look like it is made up of multiple pages, but for now let's just talk about positions and modules.

For example, one position is "left". Think of this position as a box with the name "left" that is put somewhere on the page. This position could actually be anywhere depending upon how you set up the main template page, but hopefully it will be somewhere on the left to avoid confusion.

Within a position you can place one or more modules. A module is a bit of content, for example, a menu.

The first instruction in the previous screen is saying that "mainmenu" module should be in the "left" position, and that this "mainmenu" module should have a (CSS) class suffix of "-left".