Key properties: (1) The tangent at any point makes equal angles with the focal distance and the axis. (2) The foot of the perpendicular from the focus to any tangent lies on the tangent at the vertex (the y-axis for $y^2$=4ax). (3) The portion of a tangent between the point of tangency and the directrix subtends a right angle at the focus. (4) Reflection property: a ray parallel to the axis reflects through the focus.