[definataly]

They use trilateration to know where it came from. Since there are 3 observatories (Hanford, Livingston and Virgo) the waves will arrive at slightly different amplitudes / times / angles ... which allows you to estimate where in the sky it came from.

The waves also have different shapes (frequency, amplitude, shape) which tells us about the nature of the merger.

[mmmBacon]

Your comment got me thinking about the coordinate transformation needed to triangulate the position. Having done a good bit of this as a student, I can only imagine what a nasty bit of math that must be! Makes me shudder.