Turning or steering is accomplished through carefully placed movements of the handlebars, it’s not hard per say just understanding what is happening actually can sound a bit more frightening than what you realize is going on. 

Let's start by defining the upward driving position to be the zero steering position as the motorcycle enters a corner the rider will lean the bike, first by shifting his body weight to the inside of the turn, then turns the handle bars slightly in the opposite direction. Yes I said opposite direction. This is due to gyroscopic precession, which is the direction in which the force applies with respects to the motion of the force being applied, which is ninety degrees.  This concept refers to the first of Isaac Newton’s three laws in which a object will remain in a straight forward motion unless acted upon by an outside force, the concept proves difficult for for slow speeds.
For a better understanding

I refer to another source, which I received from (http://www.reverserotatingrotors.com/mythbuster.html)

“Capirossi is in transition from left to right. His steering input changes the lean angle which causes precession to steer the front wheel to the right which

Causes the bike to stop changing lean angle. This momentarily allows him to steer back to the left which starts the cycle over until he releases pressure at the

Bars. Part of what started the wobble in this clip is that the rider aggressively changed steering input while the rear was sliding. That caused the rear tire to suddenly gain traction and quickly rotate the bike to the right. Of course that caused the front wheel to generate precession. The rider's aggressive steering input moves the contact patch forward when the bike is leaned over which effectively reduces trail. Short trail reduces steering effort at the expense of twitchy handling because it allows the rider to initiate a rapid change in lean angle. But a rapid change in lean angle only makes the torque generated by the front wheel that much greater. The mass of the bike changes lean angle with very little resistance. Because the rider must fight the torque produced by the precession of the front wheel it forces him to exert substantial energy to overcome an unnecessary force and in this instance caused a wobble.”

  
Provided courtesy of :  http://motorcyclephysics.com/motorcycle-physics-resources