Magento's logging (Debugging)

The output of  Logs written to the var/log/system.log file, which also includes the rest of the system logging output. Logging must be enabled for output to be written to this file.
You can enable logging in the Magento admin panel as,
System -> Configuration - > Developer -> Log Settings and setting 'Enabled' to True.

eg. Mage :: log("I am inside the function");

Mage::log Access the system logger
Mage::getModel Access a system model object
Mage::getStoreConfig Access the system configuration settings