The document discusses planes and distances in R3. It begins by explaining that a plane Π can be represented by a normal vector n and a reference point P0 on the plane. The equation of a plane is derived as the dot product of any point P on the plane and the normal vector n being equal to 0. Examples are given of finding the equation of a plane given information like the normal vector or three points on the plane. The document also discusses finding the distance between planes, points and lines by using properties of orthogonality and projections.