Countersteering is a gentle press of the handlebar in the direction you want to go,and a press left/press right (or vice versa) constitutes a swerve around an object! A steady constant press is an awesome ride through a sweeping curve.
IrishJohn, your "instructor" is an idiot. By telling you that you'll crash if you don't understand the science behind it inidcates that he doesn't understand his trade. You already have the subconcious ability to perform the manuver but by making it a conscious thought process, you and every other non-physics major, get wrapped around the axle by the "why". Focus on what you know by practicing what you've aready done-and after your ride re-riide it it your head...
Asphalt dancing with your 2 wheeled dancer is a lifetime of pleasure and learning-and practicing makes you all the better as you begin to turn up the tempo!