mathematics - The normal vector to a plane ax+by+cz+d=0?

I am calculating the normal vector to a plane ax+by+cz+d=0

According to the book:

The normal vector N is often normalized to unit length because in that case the equation

d = N ⋅Q + D 

gives the signed distance from the plane to an arbitrary point Q. If d = 0, then the point Q lies in the plane. If d > 0, we say that the point Q lies on the positive side of the plane since Q would be on the side in which the normal vector points.

How to get the N (Normal vector)? Thank you