it seems to b easy:
1. connect 12V to it...
2. connect wires for the output like this:
GNDsensor-----------------------wire#1-------------------100R(or similar)-----------------------wire#2-------------------OUTPUTsensor
3. calibrate the arduino (i would use the INTERNAL ADC ref, which should give u reproducible results at the same temperature/voltage):
http://arduino.cc/en/Reference/AnalogReference?from=Reference.AREF