Module's are areas in a joomla website were software or different functions can be placed...they appear in the different templates and can be assigned to different pages and positions.

If you want to see where the module positions are on a website simply enter in this code after the website name /?tp=1 and you will see at the different positions you can put software into - software like slideshows, galleries, poll's, news, feeds, login, menu

http://www.gardenrouteonline.co.za/?tp=1