A normal wood has one side heavier than the other, this gives it the ability to turn. As you bowl your wood, you should notice that it will start to curve. This means, you can't bowl your wood straight at the jack on our green. We suggest you start off by aiming for the rink markers.
On grass, the bias of a bowl is different. Usually, it doesn't require you to bowl it as wide, but does require you to bowl heavier.
It's believed that the "bias" was introduced inadvertently in 1522 by the Duke of Suffolk. Apparently his bowl split in two after striking other bowls and he took a knob off of a stairway banister post for a replacement. The flat side of the knob caused it to roll with a bias and he experimented by curving his bowl around others. The word spread and bias bowls gradually came into use.