Hi Rick,
Connect one end of LDR to ground and the other end to positive through a resistor not less than 1K.
Connect the common point of LDR and the resistor to one of the ADC pin of the ATMEGA.
Here is an example of how to use the ADC of ATMEGA16.
http://www.engineersgarage.com/embedded/avr-microcontroller-projects/adc-circuit