This motor driver board works by accepting a PWM input and using that signal to generate an output. The 5V means that the input signal must be 5.0V logic, although 3.3V will most likely work as well. As an example, if your working voltage is 12V, and you provide a 15kHz signal at a 50% duty cycle, you will effectively create a 6V output, oscillating 15000 times a second. All that this board allows you to do is to modulate the output voltage by providing a PWM input.
Regards,
Willis