Hi,

A very nice example from http://stackoverflow.com/questions/576908/how-does-magento-code-work/3581506#3581506 that always saves time:

example.com/magento/index.php/helloworld

is transparently pointing to

example.com/magento/index.php/helloworld/index/index

so basically you have the following URI structure for modules

example.com/magento/index.php/:module/:controller/:action/:param1[/:paramN ...]