Here's the circuit as scheched using Scheme-it. 

Scheme-it was easy to get this far with - only took a couple of minutes. Didn't need to log-in.

L1 is toggled on/off by Pin 12 as the reed switch gets activated and grounds Pin 2.

Adafruit is a good place to get basic Arduino tutorials. The basic interrupt code example I buit from came from the main arduino site.