How is Gyro drift error related to error in velocity and position?

"A constant error in attitude rate (gyro) results in a quadratic error in velocity and a cubic error growth in position."

How is Gyro drift error related to error in velocity and position?

In a typical pure inertial nav solution, you must cancel out the acceleration due to gravity by subtracting it out. If the vehicle's down vector is incorrect, this error appears as a lateral acceleration that is equal to $$\\sin \theta_{error}\$$ -- and for small angles is close to $$\\theta_{error}\$$ itself. So if the gyro has an offset, $$\\theta_{error}\$$ grows linearly and therefore acceleration error grows linearly (at first).