Most passing is done on the left. You may pass on the right on multi-lane or one-way roads and when overtaking a streetcar or a left-turning vehicle.
Passing on the right can be more dangerous than passing on the left. If you are driving in the left most lane with a slower vehicle in front of you, wait for the vehicle to move to the right. Do not suddenly change lanes and pass on the right; the driver in front may realize you want to pass and move to the right at the same time you do.