What do numbers in knots array mean and why do we need them? can’t clearly understand.

The knots define how the polynomial pieces are blended together with the proper smoothness.

The sequence of knots is assumed to be nondecreasing, i.e. t <= t+1. Each successive pair of knots represents an interval [t, t+1) for the parameter values to calculate a segment of a shape.

The actual values of the knots is not important, it is the relation between the knots that are used.

I suggest to take a look at this pdf

Mikael

thanks for link