Refer to figures.
Vortex Ring State (settling with power) is a hazardous flight condition which you need to understand so that you can best avoid it. It is best described as a flight condition where the disc of a descending helicopter comes into contact with its own turbulent, and compressed, wake. The result is a marked loss of thrust which can lead to an even greater, and possibly uncontrollable, rate of descent.

When the rate of descent flow increases, it will have a much larger effect on the angle of the relative airflow at the blade root than at the blade tip. At a certain value of rate of descent the angle of attack at the blade root will exceed the stalling angle first and thrust will be lost.

Towards the blade tips the angle of attack is reduced. Tip vortices will of course reduce the effective angle of attack in any state of flight, but the very strong ring vortex through which the blade tips are travelling will cause an even more pronounced reduction in the effective angle. The result is loss of thrust

Any attempt to regain thrust by raising the collective will simply cause a larger section of the blade to stall at the root end.

In most of our studies of induced flow we conveniently assume that the induced flow is constant across the disk. This is not in fact the case. Because of the higher value of V more lift is produced at the tips than at the root - despite the countering effect of blade washout. More lift means more induced flow, so the induced flow will actually be greater at the tips than at the root. This further adds to the difference in angle of attack between root and tip.