how do modules work?

i'm using Simple HTML module as an example. when i installed it no original files were overwritten but once installed and enabled from admin it can load itself into the left, right or middle columns on the storefront. how does it do that? how does it install? what controls how its positioned and where its placed on the storefront? im a newb obviously so as much detail as possible or links to how opencart works would be greatly appreciated.

Simple HTML module is available at http://www.opencart.com/index.php?route ... ad_id=4997

well if you are not a programmer it's going to be a bit difficult to understand. The admin scans the module directory and then lists all those files on the module page. When you click the install button it adds the module to the extensions table of the database and runs the install function from the module if one exists. Then when you click edit and see all the options those are all stored in the settings table including the position. then on the front end of the site the various places a module can reside left column right column and home page all check the database to see if there are any modules enabled to reside in that position and display them according to the sort order set in the module that is stored in the settings table.