Separate each vector into its x, y, and z components.
For example, the functional form of a vector field might be xy x-hat, x y-hat, (1-y)z^2 z-hat. The term "x-hat" refers to a unit vector in the direction of x; likewise for the other coordinates. So "xy x-hat" refers to a vector that has a magnitude of x times y in the direction of x.
Take the derivative of each component with respect to its direction. That is, take the derivative of the x-component with respect to x, and so on for the other components.
The derivatives for the example function are (d/dx)(xy) = y, (d/dy)(x) = 0, (d/dz)(1-y)z^2 = 2z(1-y).
Add the derivatives together to get the divergence.
For the example, the sum is y + 0 + 2z(1-y) = y + 2z(1-y).
Calculate the value of divergence for the values of interest in the field.
In this example, for every value of x at y=0, the divergence is 2z, while for every value of x at y=1, the divergence is 1.