How convert a voltage signal into speed?

Hi guys,
I have bought an anemometer for Arduino on Amazon but I have a problem…It returns a voltage signal or a current signal. How can I convert these value into wind speed?

this is the anemometer:

--> Wind_Speed_Sensor_Voltage_Type_0-5V__SKU_SEN0170-DFRobot

Mount the anemometer on an automobile, and measure the signal when you drive around at different speeds.

Best to do this on a windless day.

Calibrate by following this tutorial on sensor calibration.