Batt-PWM-receiver module-motor

I received the 10A PWM today to slow my 3A motor discussed in previous posts. A couple of sources of confusion:
I connected the PWM inputs from 12v battery and read output voltage to motor. Adjusting the PWM dial, voltage went from 12.87v down to 12.53v. Doesn’t seem right or does it modulate amperage rather than voltage?
Since the PWM only has +/- inputs from battery and +/- out puts to motor, how to I insert the receiver into the flow since it has inputs from battery and outputs to motor also? Do the outputs from the PWM become inputs to receiver? Guessing so but don’t wish to smoke either or both components. “Input” appreciated.

I have my answer. Had purchased two of these PEMs so figured wth. Performs very well throughout the range. Google gave me answers to the first question.

Finger fudged P”E”M (PWM)