If you need some tips make sure you back up a bit, don't stare too close.. when you start to cross your eyes you'll see the left and right image and a 3rd in the middle, focus on the 3rd image in the middle and it should pop into 3D... If you're too far back it will be hard, and if you're too close it will be hard, so try moving your head near/far accordingly until it snaps into place.
Pretty cool !