Joomla works on positions. Position works as a placeholder in Joomla Template where we place a module. According to those positions Joomla application able to place the module to a particular portion of a page. For example, the module position left means the module will display at the left position defined in template and module position right means module will display at the right position of the template. So if the module assigned left position that does not mean it will display at the left end. It will display the module wherever the designer place left module position.
Position can be defined in two ways:
you can define the position in the xml file of the template.
You can also define the custom position by simply writing the position in the module position field through the admin section.
After defining the position you will include those positions to the index.php file of the template.