Need Explanation on Triangulation

Hi..
I'm building a sound sensing robot, similar to this one in the link..

Cornell's Autonomous PeanutBot

I want to use the method of triangulation they have used, for finding the sound source..

However, i did not understand the concept...

Can anyone explain me the concept of triangulation using microphones that they have used, in detail?

I have read the IR triangulation method, but did not quite get it either...

So, please help me out..

Thank You..