When using a microcontroller one of the most important feature to use is the internal non-volatile memory. This will allow you to store information that might be needed to store user selected features or system variables that need to persist power cycling. Interfacing with the EEPROM will depend on the microcontroller you are using. In this case it is an Atmega168.
Our friend Daniel Garcia from Prostack has put together an article that shows us how to Read and Write to the Atmega168 internal EEPROM.