This will likely come naturally, but just in case you don't get this, the easiest way is to start the first episode, about Grizzly Bears. When you get to the first sidetrack part the first answer is the right path, so hold up your right hand. The 2nd answer is the left paw, so hold up your left hand. Achievement should pop once you get the 2nd answer right. If you can manage to get all sidetrack answers correct in an episode, you'll also earn:
The Triple Tracker achievement in Kinect Nat Geo TV worth 46 pointsWithout ever stopping an episode, earn all of its Sidetrack stars (or watch someone do this).