It will randomly choose a location and determine if it falls within the circle. Do this enough times, you can approximate pi! Program is currently set to 1000 times, is it more accurate if you change it to 10000? For the math and a more thorough description, please see: http://interactivepython.org/courselib/static/thinkcspy/Labs/montepi.html
http://interactivepython.org/courselib/static/thinkcspy/Labs/montepi.html