Refer to figures.
The drag that acts on the blades during their angular movement along their plane of rotation, attempts to decelerate them. The point of maximum drag will be experienced by the blade when its angular velocity is greatest, in the advancing side.

These acceleration-deceleration forces are transmitted to the blade hub attachment points and are flet as large lateral bending stresses. If the blade is rigidly attached to the hub, the bending stresses could be enough to break the blade.

The solution in this case is the lead-lad hinges or dragging hinges, which allow the blade to move slightly forward (lead) or slightly rearwards (lag) along the plane of rotation.

Alternatively, some helicopter types, instead of dragging hinges, use blades with very strong roots and attachment components.

But the hinge alone will not reduce or absorb the lateral loads. This can be performed by an associated drag damping device.

The drag dampers absorb most of the lateral loads imposed by acceleration and deceleration, prevent the blade for banging against the hinge stops and reduces the vibration which would otherwise be caused by the constantly changing forces on the blade.

Plane Of Rotation (PoR), or Hub Plane of rotation, is a line extended from the rotor hub, through its centre, parallel to the Tip Path Plane, and perpendicular to the Axis Of Rotation. On the ground, when the blades are not producing lift, the POR coincides with the Tip Path Plane.

Once you increase the pitch and start creating lift, the blades (and TPP) rise into the air. As they form an inverted cone with its apex at the rotor shaft, the angular difference is the coning angle.