Joomla modules are an additional tool to extend the functionality of any site. Basically, the main task of any module is to display the required information and add installed components on the site. They can be placed in any position of the site, provided the layout of the template. An example of the modules is the navigation menu, calendar, list of popular articles, etc.when you publish the module, you can specify in which position the site template and on which pages it will be displayed. In addition, most of the modules installed on the system can be copied and published several times with different parameters.
Joomla modules - ArenaM - Extension development