Deriving equations from the MOSFET Characteristics curve

[khatus]

Hello Guys,
I can't understand some parts of the MOSFET static characteristics curve. Here the equation given for the Triode region for the characteristics curve of the MOSFET is VP≤ VGS ≤ 0 and
VDS ≤ VGS-VP. My question is How I can find these two equations by looking at the graph? Or it would be better if someone could explain how to determine these two equations by analyzing the graph shown in the picture.